diff --git a/README.md b/README.md
index 3ba7545..9f3d11a 100644
--- a/README.md
+++ b/README.md
@@ -163,13 +163,26 @@ Key settings:
   `YYYY-MM-DD` are listed automatically.
   If a yearly subfolder exists (for example `.../2026/`), it is preferred.
 
-- **calendar_ics_files**
-  Local calendar `.ics` files (one absolute file path per line).
-  Events are parsed by `sabre/vobject` and shown on matching chronological day pages.
-  Recurrence and exclusions from the ICS are respected. For timed entries, the
-  page stores the original timestamp and renders the visible time in the
-  browser's local timezone.
-  Multi-day events appear on each overlapping day.
+- **calendar_ics_files** (REMOVED — replaced by per-slot calendar configuration)
+
+- **Calendar Slots** (configured via Admin -> luxtools)
+  The plugin supports 4 calendar slots: `general`, `maintenance`, `slot3`, `slot4`.
+  Each slot has its own settings:
+
+  - **File**: Local `.ics` file path
+  - **CalDAV URL**: Remote CalDAV collection URL (optional)
+  - **Username**: CalDAV authentication username
+  - **Password**: CalDAV authentication password
+  - **Color**: CSS color for calendar widget indicators
+
+  A slot is enabled if it has a local file path or a CalDAV URL configured.
+  The old `calendar_ics_files` setting has been replaced by the `general` slot's file path.
+
+  Default colors:
+  - general: `#4a90d9` (blue)
+  - maintenance: `#e67e22` (orange)
+  - slot3: `#27ae60` (green)
+  - slot4: `#8e44ad` (purple)
 
 - **pagelink_search_depth**
   Maximum directory depth for `.pagelink` discovery under each configured root.
@@ -287,6 +300,10 @@ Notes:
 - Month switches fetch server-rendered widget HTML via AJAX and replace only the widget node.
 - Calendar output is marked as non-cacheable to keep missing/existing link styling and
   current-day highlighting up to date.
+- Each day cell shows colored corner indicators for calendar slots that have events on that day.
+  Indicator positions (clockwise): general = top-left, maintenance = top-right,
+  slot3 = bottom-right, slot4 = bottom-left.
+  Indicator colors are taken from the slot's configured color.
 
 ### 0.4) Virtual chronological day pages
 
@@ -297,7 +314,8 @@ default "page does not exist" output.
 The virtual page includes:
 
 - a German-formatted heading (for example `Freitag, 13. Februar 2026`)
-- matching local calendar events from configured `.ics` files (when available)
+- matching calendar events from all enabled calendar slots (grouped by slot)
+- maintenance tasks with completion buttons (from the maintenance slot)
 - matching day photos (via existing `{{images>...}}` rendering) when available
 
 The page is only created once you edit and save actual content.
@@ -314,6 +332,90 @@ luxtools provides an admin-only **Invalidate Cache** action in the page tools me
   permission errors).
 - Also useful when actively adding external photos to the current day page.
 
+### 0.6) Multi-calendar slot system
+
+The plugin supports 4 calendar slots, each with independent configuration for
+a local `.ics` file, CalDAV URL, authentication, and display color.
+
+- **general**: The default event calendar. Events appear on day pages like before.
+- **maintenance**: A task-oriented calendar. Events are treated as tasks with
+  completion tracking. Tasks can be marked complete/reopened via buttons on day pages.
+- **slot3**, **slot4**: Reserved for future use. Events from these slots appear
+  on day pages with the slot's label as the section heading.
+
+Calendar data is always read from local `.ics` files for rendering. If a remote
+CalDAV source is configured, use the sync feature to populate the local file.
+
+### 0.7) Maintenance task completion
+
+Maintenance tasks shown on day pages include a "Complete" button. Clicking it:
+
+1. Updates the event's `STATUS` property in the local `.ics` file.
+2. If the maintenance slot has a CalDAV URL configured, also updates the remote
+   calendar object.
+3. Shows visual feedback and reports any remote write failures.
+
+Completed tasks can be reopened with a "Reopen" button.
+
+Write-back rules:
+- `VEVENT` components: `STATUS:TODO` for open, `STATUS:COMPLETED` for completed.
+- `VTODO` components: Uses native completion semantics (`STATUS:COMPLETED`,
+  `COMPLETED` timestamp, `PERCENT-COMPLETE:100`).
+- Recurring events: Completion writes an occurrence override/exception to preserve
+  per-occurrence state rather than modifying the master event.
+
+### 0.8) Event popup
+
+Clicking any event on a day page opens a popup overlay showing:
+- Title
+- Date/time (formatted in the browser's locale)
+- Location (if available)
+- Description (if available)
+- Calendar slot name
+
+Close the popup by clicking outside it or pressing Escape.
+
+### 0.9) Maintenance task list syntax
+
+Embed a list of open maintenance tasks anywhere on a wiki page:
+
+```
+{{maintenance_tasks>}}
+```
+
+This renders all non-completed maintenance tasks due today or earlier, sorted
+with overdue tasks first (then by date, time, and title).
+
+Each task shows its date, optional time, summary, and a "Complete" button.
+
+### 0.10) CalDAV sync
+
+If a slot has a CalDAV URL configured, the admin panel provides a sync button.
+Triggering sync downloads all calendar objects from the remote CalDAV collection
+and merges them into the slot's local `.ics` file.
+
+Sync is admin-only and does not run automatically. For scheduled sync, set up
+a cron job that triggers the sync via the DokuWiki AJAX endpoint.
+
+### Known limitations
+
+- **Recurring event completion write-back**: For recurring events, completing a
+  single occurrence writes an override/exception component to the `.ics` file.
+  This works well for simple `RRULE` patterns. Some CalDAV servers may handle
+  the override differently. If the override is rejected by the remote server,
+  the local file will still have the correct state, but remote sync may
+  overwrite it on next sync.
+
+- **Sync direction**: Sync is currently one-directional (remote → local). Local
+  changes made via task completion are written back to the remote individually,
+  but a full remote-to-local sync may overwrite local changes if the remote
+  still has stale data. The completion write-back updates the remote immediately
+  to mitigate this.
+
+- **VTODO recurrence**: sabre/vobject's recurrence expansion has limited support
+  for `VTODO` components. Recurring `VTODO` items may not expand as expected.
+  Non-recurring `VTODO` items work correctly.
+
 ### 1) List files by glob pattern
 
 The `{{directory>...}}` syntax (or `{{files>...}}` for backwards compatibility) can handle both directory listings and glob patterns. When a glob pattern is used, it renders as a table:
diff --git a/action.php b/action.php
index d047f77..a0d7c4c 100644
--- a/action.php
+++ b/action.php
@@ -4,11 +4,15 @@ use dokuwiki\Extension\ActionPlugin;
 use dokuwiki\Extension\Event;
 use dokuwiki\Extension\EventHandler;
 use dokuwiki\plugin\luxtools\CacheInvalidation;
+use dokuwiki\plugin\luxtools\CalDavClient;
+use dokuwiki\plugin\luxtools\CalendarEvent;
+use dokuwiki\plugin\luxtools\CalendarService;
+use dokuwiki\plugin\luxtools\CalendarSlot;
 use dokuwiki\plugin\luxtools\ChronoID;
 use dokuwiki\plugin\luxtools\ChronologicalCalendarWidget;
 use dokuwiki\plugin\luxtools\ChronologicalDateAutoLinker;
 use dokuwiki\plugin\luxtools\ChronologicalDayTemplate;
-use dokuwiki\plugin\luxtools\ChronologicalIcsEvents;
+use dokuwiki\plugin\luxtools\IcsWriter;
 use dokuwiki\plugin\luxtools\MenuItem\InvalidateCache;
 require_once(__DIR__ . '/autoload.php');
 
@@ -65,6 +69,18 @@ class action_plugin_luxtools extends ActionPlugin
             $this,
             "handleCalendarWidgetAjax",
         );
+        $controller->register_hook(
+            "AJAX_CALL_UNKNOWN",
+            "BEFORE",
+            $this,
+            "handleMaintenanceTaskAction",
+        );
+        $controller->register_hook(
+            "AJAX_CALL_UNKNOWN",
+            "BEFORE",
+            $this,
+            "handleCalendarSyncAction",
+        );
         $controller->register_hook(
             "ACTION_ACT_PREPROCESS",
             "BEFORE",
@@ -105,6 +121,7 @@ class action_plugin_luxtools extends ActionPlugin
             "page-link.js",
             "linkfavicon.js",
             "calendar-widget.js",
+            "event-popup.js",
             "main.js",
         ];
 
@@ -147,7 +164,18 @@ class action_plugin_luxtools extends ActionPlugin
 
         $this->sendNoStoreHeaders();
 
-        $html = ChronologicalCalendarWidget::render($year, $month, $baseNs);
+        // Load slot indicators and colors for the calendar widget
+        $slots = CalendarSlot::loadEnabled($this);
+        $indicators = CalendarService::monthIndicators($slots, $year, $month);
+        $slotColors = [];
+        foreach ($slots as $slot) {
+            $color = $slot->getColor();
+            if ($color !== '') {
+                $slotColors[$slot->getKey()] = $color;
+            }
+        }
+
+        $html = ChronologicalCalendarWidget::render($year, $month, $baseNs, $indicators, $slotColors);
         if ($html === '') {
             http_status(500);
             echo 'Calendar rendering failed';
@@ -458,50 +486,348 @@ class action_plugin_luxtools extends ActionPlugin
     /**
      * Render local calendar events section for a given date.
      *
+     * Uses the slot-aware CalendarService to render events from all enabled slots.
+     *
      * @param string $dateIso
      * @return string
      */
     protected function renderChronologicalEventsHtml(string $dateIso): string
     {
-        $icsConfig = (string)$this->getConf('calendar_ics_files');
-        if (trim($icsConfig) === '') return '';
+        $slots = CalendarSlot::loadEnabled($this);
+        if ($slots === []) return '';
 
-        $events = ChronologicalIcsEvents::eventsForDate($icsConfig, $dateIso);
-        if ($events === []) return '';
+        $grouped = CalendarService::eventsForDateGrouped($slots, $dateIso);
+        if ($grouped === []) return '';
 
-        $title = (string)$this->getLang('chronological_events_title');
-        if ($title === '') $title = 'Events';
+        $html = '';
 
-        $items = '';
-        foreach ($events as $entry) {
-            $summary = trim((string)($entry['summary'] ?? ''));
-            if ($summary === '') $summary = '(ohne Titel)';
+        // Render general events
+        if (isset($grouped['general'])) {
+            $title = (string)$this->getLang('chronological_events_title');
+            if ($title === '') $title = 'Events';
+            $html .= $this->renderEventSection($grouped['general'], $title, 'general');
+        }
 
-            $time = trim((string)($entry['time'] ?? ''));
-            $startIso = trim((string)($entry['startIso'] ?? ''));
-            $isAllDay = (bool)($entry['allDay'] ?? false);
+        // Render maintenance tasks
+        if (isset($grouped['maintenance'])) {
+            $title = (string)$this->getLang('chronological_maintenance_title');
+            if ($title === '') $title = 'Tasks';
+            $html .= $this->renderMaintenanceSection($grouped['maintenance'], $title, $dateIso);
+        }
 
-            if ($isAllDay || $time === '') {
-                $items .= '<li>' . hsc($summary) . '</li>';
-            } else {
-                $timeHtml = '<span class="luxtools-event-time"';
-                if ($startIso !== '') {
-                    $timeHtml .= ' data-luxtools-start="' . hsc($startIso) . '"';
-                }
-                $timeHtml .= '>' . hsc($time) . '</span>';
-                $items .= '<li>' . $timeHtml . ' - ' . hsc($summary) . '</li>';
+        // Render slot3/slot4 if present
+        foreach (['slot3', 'slot4'] as $slotKey) {
+            if (isset($grouped[$slotKey]) && isset($slots[$slotKey])) {
+                $label = $slots[$slotKey]->getLabel();
+                $html .= $this->renderEventSection($grouped[$slotKey], $label, $slotKey);
             }
         }
 
-        if ($items === '') return '';
-        $html = '<ul>' . $items . '</ul>';
+        return $html;
+    }
 
-        return '<div class="luxtools-plugin luxtools-chronological-events">'
+    /**
+     * Render a section of events for a given slot.
+     *
+     * @param CalendarEvent[] $events
+     * @param string $title
+     * @param string $slotKey
+     * @return string
+     */
+    protected function renderEventSection(array $events, string $title, string $slotKey): string
+    {
+        $items = '';
+        foreach ($events as $event) {
+            $items .= $this->renderEventListItem($event);
+        }
+        if ($items === '') return '';
+
+        return '<div class="luxtools-plugin luxtools-chronological-events luxtools-slot-' . hsc($slotKey) . '">'
             . '<h2>' . hsc($title) . '</h2>'
-            . $html
+            . '<ul>' . $items . '</ul>'
             . '</div>';
     }
 
+    /**
+     * Render a maintenance task section with completion buttons.
+     *
+     * @param CalendarEvent[] $events
+     * @param string $title
+     * @param string $dateIso
+     * @return string
+     */
+    protected function renderMaintenanceSection(array $events, string $title, string $dateIso): string
+    {
+        $items = '';
+        $ajaxUrl = defined('DOKU_BASE') ? (string)DOKU_BASE . 'lib/exe/ajax.php' : 'lib/exe/ajax.php';
+
+        foreach ($events as $event) {
+            $items .= $this->renderMaintenanceListItem($event, $ajaxUrl);
+        }
+        if ($items === '') return '';
+
+        $secToken = function_exists('getSecurityToken') ? getSecurityToken() : '';
+
+        return '<div class="luxtools-plugin luxtools-chronological-events luxtools-chronological-maintenance"'
+            . ' data-luxtools-ajax-url="' . hsc($ajaxUrl) . '"'
+            . ' data-luxtools-sectok="' . hsc($secToken) . '">'
+            . '<h2>' . hsc($title) . '</h2>'
+            . '<ul>' . $items . '</ul>'
+            . '</div>';
+    }
+
+    /**
+     * Render a single event as a list item with popup data attributes.
+     *
+     * @param CalendarEvent $event
+     * @return string
+     */
+    protected function renderEventListItem(CalendarEvent $event): string
+    {
+        $summaryHtml = hsc($event->summary);
+
+        // Build event detail data attributes for popup
+        $dataAttrs = ' data-luxtools-event="1"';
+        $dataAttrs .= ' data-event-summary="' . hsc($event->summary) . '"';
+        $dataAttrs .= ' data-event-start="' . hsc($event->startIso) . '"';
+        if ($event->endIso !== '') {
+            $dataAttrs .= ' data-event-end="' . hsc($event->endIso) . '"';
+        }
+        if ($event->location !== '') {
+            $dataAttrs .= ' data-event-location="' . hsc($event->location) . '"';
+        }
+        if ($event->description !== '') {
+            $dataAttrs .= ' data-event-description="' . hsc($event->description) . '"';
+        }
+        $dataAttrs .= ' data-event-allday="' . ($event->allDay ? '1' : '0') . '"';
+        $dataAttrs .= ' data-event-slot="' . hsc($event->slotKey) . '"';
+
+        if ($event->allDay || $event->time === '') {
+            return '<li' . $dataAttrs . '><span class="luxtools-event-summary">' . $summaryHtml . '</span></li>';
+        }
+
+        $timeHtml = '<span class="luxtools-event-time" data-luxtools-start="' . hsc($event->startIso) . '">'
+            . hsc($event->time) . '</span>';
+        return '<li' . $dataAttrs . '>' . $timeHtml . ' - <span class="luxtools-event-summary">' . $summaryHtml . '</span></li>';
+    }
+
+    /**
+     * Render a maintenance task as a list item with completion button.
+     *
+     * @param CalendarEvent $event
+     * @param string $ajaxUrl
+     * @return string
+     */
+    protected function renderMaintenanceListItem(CalendarEvent $event, string $ajaxUrl): string
+    {
+        $isCompleted = $event->isCompleted();
+        $classes = 'luxtools-maintenance-task';
+        if ($isCompleted) $classes .= ' luxtools-task-completed';
+
+        $summaryHtml = hsc($event->summary);
+
+        // Data attributes for popup and completion
+        $dataAttrs = ' data-luxtools-event="1"';
+        $dataAttrs .= ' data-event-summary="' . hsc($event->summary) . '"';
+        $dataAttrs .= ' data-event-start="' . hsc($event->startIso) . '"';
+        if ($event->endIso !== '') {
+            $dataAttrs .= ' data-event-end="' . hsc($event->endIso) . '"';
+        }
+        if ($event->location !== '') {
+            $dataAttrs .= ' data-event-location="' . hsc($event->location) . '"';
+        }
+        if ($event->description !== '') {
+            $dataAttrs .= ' data-event-description="' . hsc($event->description) . '"';
+        }
+        $dataAttrs .= ' data-event-allday="' . ($event->allDay ? '1' : '0') . '"';
+        $dataAttrs .= ' data-event-slot="maintenance"';
+        $dataAttrs .= ' data-task-uid="' . hsc($event->uid) . '"';
+        $dataAttrs .= ' data-task-date="' . hsc($event->dateIso) . '"';
+        $dataAttrs .= ' data-task-recurrence="' . hsc($event->recurrenceId) . '"';
+        $dataAttrs .= ' data-task-status="' . hsc($event->status) . '"';
+
+        $buttonLabel = $isCompleted
+            ? (string)$this->getLang('maintenance_task_reopen')
+            : (string)$this->getLang('maintenance_task_complete');
+        if ($buttonLabel === '') $buttonLabel = $isCompleted ? 'Reopen' : 'Complete';
+        $buttonAction = $isCompleted ? 'reopen' : 'complete';
+
+        $buttonHtml = '<button type="button" class="luxtools-task-action" data-action="' . hsc($buttonAction) . '">'
+            . hsc($buttonLabel) . '</button>';
+
+        $timeHtml = '';
+        if (!$event->allDay && $event->time !== '') {
+            $timeHtml = '<span class="luxtools-event-time" data-luxtools-start="' . hsc($event->startIso) . '">'
+                . hsc($event->time) . '</span> - ';
+        }
+
+        return '<li class="' . hsc($classes) . '"' . $dataAttrs . '>'
+            . $timeHtml
+            . '<span class="luxtools-event-summary">' . $summaryHtml . '</span> '
+            . $buttonHtml
+            . '</li>';
+    }
+
+    /**
+     * Handle AJAX requests for marking maintenance tasks complete/reopen.
+     *
+     * @param Event $event
+     * @param mixed $param
+     * @return void
+     */
+    public function handleMaintenanceTaskAction(Event $event, $param)
+    {
+        if ($event->data !== 'luxtools_maintenance_task') return;
+
+        $event->preventDefault();
+        $event->stopPropagation();
+
+        header('Content-Type: application/json; charset=utf-8');
+        $this->sendNoStoreHeaders();
+
+        global $INPUT;
+
+        // Verify security token
+        if (!checkSecurityToken()) {
+            http_status(403);
+            echo json_encode(['ok' => false, 'error' => 'Security token mismatch']);
+            return;
+        }
+
+        $action = $INPUT->str('action'); // 'complete' or 'reopen'
+        $uid = $INPUT->str('uid');
+        $dateIso = $INPUT->str('date');
+        $recurrence = $INPUT->str('recurrence');
+
+        if (!in_array($action, ['complete', 'reopen'], true)) {
+            http_status(400);
+            echo json_encode(['ok' => false, 'error' => 'Invalid action']);
+            return;
+        }
+        if ($uid === '' || !ChronoID::isIsoDate($dateIso)) {
+            http_status(400);
+            echo json_encode(['ok' => false, 'error' => 'Missing uid or date']);
+            return;
+        }
+
+        $slots = CalendarSlot::loadAll($this);
+        $maintenanceSlot = $slots['maintenance'] ?? null;
+        if ($maintenanceSlot === null || !$maintenanceSlot->isEnabled()) {
+            http_status(400);
+            echo json_encode(['ok' => false, 'error' => 'Maintenance calendar not configured']);
+            return;
+        }
+
+        $newStatus = ($action === 'complete') ? 'COMPLETED' : 'TODO';
+
+        // Update local ICS file
+        $localOk = false;
+        $file = $maintenanceSlot->getFile();
+        if ($file !== '' && is_file($file)) {
+            $localOk = IcsWriter::updateEventStatus($file, $uid, $recurrence, $newStatus, $dateIso);
+        }
+
+        if (!$localOk) {
+            http_status(500);
+            echo json_encode(['ok' => false, 'error' => $this->getLang('maintenance_complete_error')]);
+            return;
+        }
+
+        // Clear caches so next render picks up changes
+        CalendarService::clearCache();
+
+        // Remote CalDAV write-back if configured
+        $remoteOk = true;
+        $remoteError = '';
+        if ($maintenanceSlot->hasRemoteSource()) {
+            try {
+                $caldavOk = CalDavClient::updateEventStatus(
+                    $maintenanceSlot->getCaldavUrl(),
+                    $maintenanceSlot->getUsername(),
+                    $maintenanceSlot->getPassword(),
+                    $uid,
+                    $recurrence,
+                    $newStatus,
+                    $dateIso
+                );
+                if (!$caldavOk) {
+                    $remoteOk = false;
+                    $remoteError = $this->getLang('maintenance_remote_write_failed');
+                }
+            } catch (Throwable $e) {
+                $remoteOk = false;
+                $remoteError = $this->getLang('maintenance_remote_write_failed');
+            }
+        }
+
+        $msg = ($action === 'complete')
+            ? $this->getLang('maintenance_complete_success')
+            : $this->getLang('maintenance_reopen_success');
+
+        echo json_encode([
+            'ok' => true,
+            'message' => $msg,
+            'remoteOk' => $remoteOk,
+            'remoteError' => $remoteError,
+        ]);
+    }
+
+    /**
+     * Handle AJAX requests for manual calendar sync.
+     *
+     * @param Event $event
+     * @param mixed $param
+     * @return void
+     */
+    public function handleCalendarSyncAction(Event $event, $param)
+    {
+        if ($event->data !== 'luxtools_calendar_sync') return;
+
+        $event->preventDefault();
+        $event->stopPropagation();
+
+        header('Content-Type: application/json; charset=utf-8');
+        $this->sendNoStoreHeaders();
+
+        global $INPUT;
+
+        if (!checkSecurityToken()) {
+            http_status(403);
+            echo json_encode(['ok' => false, 'error' => 'Security token mismatch']);
+            return;
+        }
+
+        if (!function_exists('auth_isadmin') || !auth_isadmin()) {
+            http_status(403);
+            echo json_encode(['ok' => false, 'error' => 'Admin access required']);
+            return;
+        }
+
+        $slots = CalendarSlot::loadEnabled($this);
+        $results = [];
+        $hasErrors = false;
+
+        foreach ($slots as $slot) {
+            if (!$slot->hasRemoteSource()) continue;
+
+            $ok = CalDavClient::syncSlot($slot);
+            $results[$slot->getKey()] = $ok;
+            if (!$ok) $hasErrors = true;
+        }
+
+        CalendarService::clearCache();
+
+        $msg = $hasErrors
+            ? $this->getLang('calendar_sync_partial')
+            : $this->getLang('calendar_sync_success');
+
+        echo json_encode([
+            'ok' => !$hasErrors,
+            'message' => $msg,
+            'results' => $results,
+        ]);
+    }
+
     /**
      * Build wiki bullet list for local calendar events.
      *
@@ -510,23 +836,20 @@ class action_plugin_luxtools extends ActionPlugin
      */
     protected function buildChronologicalEventsWiki(string $dateIso): string
     {
-        $icsConfig = (string)$this->getConf('calendar_ics_files');
-        if (trim($icsConfig) === '') return '';
+        $slots = CalendarSlot::loadEnabled($this);
+        if ($slots === []) return '';
 
-        $events = ChronologicalIcsEvents::eventsForDate($icsConfig, $dateIso);
+        $events = CalendarService::eventsForDate($slots, $dateIso);
         if ($events === []) return '';
 
         $lines = [];
         foreach ($events as $event) {
-            $summary = trim((string)($event['summary'] ?? ''));
-            if ($summary === '') $summary = '(ohne Titel)';
-            $summary = str_replace(["\n", "\r"], ' ', $summary);
+            $summary = str_replace(["\n", "\r"], ' ', $event->summary);
 
-            $time = trim((string)($event['time'] ?? ''));
-            if ((bool)($event['allDay'] ?? false) || $time === '') {
+            if ($event->allDay || $event->time === '') {
                 $lines[] = '  * ' . $summary;
             } else {
-                $lines[] = '  * ' . $time . ' - ' . $summary;
+                $lines[] = '  * ' . $event->time . ' - ' . $summary;
             }
         }
 
diff --git a/admin/main.php b/admin/main.php
index e77f66a..61388d6 100644
--- a/admin/main.php
+++ b/admin/main.php
@@ -8,6 +8,9 @@ if (!defined('DOKU_INC')) die();
 
 class admin_plugin_luxtools_main extends DokuWiki_Admin_Plugin
 {
+    /** @var string[] Calendar slot keys */
+    protected $calendarSlotKeys = ['general', 'maintenance', 'slot3', 'slot4'];
+
     /** @var string[] */
     protected $configKeys = [
         'paths',
@@ -29,7 +32,26 @@ class admin_plugin_luxtools_main extends DokuWiki_Admin_Plugin
         'gallery_thumb_scale',
         'open_service_url',
         'image_base_path',
-        'calendar_ics_files',
+        'calendar_general_file',
+        'calendar_general_caldav_url',
+        'calendar_general_username',
+        'calendar_general_password',
+        'calendar_general_color',
+        'calendar_maintenance_file',
+        'calendar_maintenance_caldav_url',
+        'calendar_maintenance_username',
+        'calendar_maintenance_password',
+        'calendar_maintenance_color',
+        'calendar_slot3_file',
+        'calendar_slot3_caldav_url',
+        'calendar_slot3_username',
+        'calendar_slot3_password',
+        'calendar_slot3_color',
+        'calendar_slot4_file',
+        'calendar_slot4_caldav_url',
+        'calendar_slot4_username',
+        'calendar_slot4_password',
+        'calendar_slot4_color',
         'pagelink_search_depth',
     ];
 
@@ -90,9 +112,14 @@ class admin_plugin_luxtools_main extends DokuWiki_Admin_Plugin
         $newConf['open_service_url'] = $INPUT->str('open_service_url');
         $newConf['image_base_path'] = $INPUT->str('image_base_path');
 
-        $icsFiles = $INPUT->str('calendar_ics_files');
-        $icsFiles = str_replace(["\r\n", "\r"], "\n", $icsFiles);
-        $newConf['calendar_ics_files'] = $icsFiles;
+        // Calendar slot settings
+        foreach ($this->calendarSlotKeys as $slot) {
+            $newConf['calendar_' . $slot . '_file'] = trim($INPUT->str('calendar_' . $slot . '_file'));
+            $newConf['calendar_' . $slot . '_caldav_url'] = trim($INPUT->str('calendar_' . $slot . '_caldav_url'));
+            $newConf['calendar_' . $slot . '_username'] = trim($INPUT->str('calendar_' . $slot . '_username'));
+            $newConf['calendar_' . $slot . '_password'] = trim($INPUT->str('calendar_' . $slot . '_password'));
+            $newConf['calendar_' . $slot . '_color'] = trim($INPUT->str('calendar_' . $slot . '_color'));
+        }
 
         $depth = (int)$INPUT->int('pagelink_search_depth');
         if ($depth < 0) $depth = 0;
@@ -240,11 +267,38 @@ class admin_plugin_luxtools_main extends DokuWiki_Admin_Plugin
         echo '<input type="text" class="edit" name="image_base_path" value="' . hsc((string)$this->getConf('image_base_path')) . '" />';
         echo '</label><br />';
 
-        // calendar_ics_files
-        $icsFiles = $this->normalizeMultilineDisplay((string)$this->getConf('calendar_ics_files'), 'calendar_ics_files');
-        echo '<label class="block"><span>' . hsc($this->getLang('calendar_ics_files')) . '</span><br />';
-        echo '<textarea name="calendar_ics_files" rows="4" cols="80" class="edit">' . hsc($icsFiles) . '</textarea>';
-        echo '</label><br />';
+        // Calendar slot settings
+        $slotLabels = [
+            'general' => 'General',
+            'maintenance' => 'Maintenance',
+            'slot3' => 'Slot 3',
+            'slot4' => 'Slot 4',
+        ];
+        foreach ($this->calendarSlotKeys as $slot) {
+            echo '<h2>' . hsc($this->getLang('calendar_slot_heading') . ': ' . $slotLabels[$slot]) . '</h2>';
+
+            $prefix = 'calendar_' . $slot . '_';
+
+            echo '<label class="block"><span>' . hsc($this->getLang('calendar_slot_file')) . '</span> ';
+            echo '<input type="text" class="edit" name="' . hsc($prefix . 'file') . '" value="' . hsc((string)$this->getConf($prefix . 'file')) . '" />';
+            echo '</label><br />';
+
+            echo '<label class="block"><span>' . hsc($this->getLang('calendar_slot_caldav_url')) . '</span> ';
+            echo '<input type="text" class="edit" name="' . hsc($prefix . 'caldav_url') . '" value="' . hsc((string)$this->getConf($prefix . 'caldav_url')) . '" />';
+            echo '</label><br />';
+
+            echo '<label class="block"><span>' . hsc($this->getLang('calendar_slot_username')) . '</span> ';
+            echo '<input type="text" class="edit" name="' . hsc($prefix . 'username') . '" value="' . hsc((string)$this->getConf($prefix . 'username')) . '" />';
+            echo '</label><br />';
+
+            echo '<label class="block"><span>' . hsc($this->getLang('calendar_slot_password')) . '</span> ';
+            echo '<input type="password" class="edit" name="' . hsc($prefix . 'password') . '" value="' . hsc((string)$this->getConf($prefix . 'password')) . '" />';
+            echo '</label><br />';
+
+            echo '<label class="block"><span>' . hsc($this->getLang('calendar_slot_color')) . '</span> ';
+            echo '<input type="color" name="' . hsc($prefix . 'color') . '" value="' . hsc((string)$this->getConf($prefix . 'color') ?: '#999999') . '" />';
+            echo '</label><br />';
+        }
 
         // pagelink_search_depth
         echo '<label class="block"><span>' . hsc($this->getLang('pagelink_search_depth')) . '</span> ';
diff --git a/agents.md b/agents.md
index da5b241..3a87402 100644
--- a/agents.md
+++ b/agents.md
@@ -23,4 +23,4 @@
 # Conduct and user interactions
 - The user is a professional software developer, but unfamiliar with Dokuwiki internals, PHP and JavaScript best practices
 - When the user gives specific instructions regarding implementation details, check wether those details fit PHP and Dokuwiki best practices.
-- If the user instructions conflict with best practices, point out the conflict and suggest alternatives
\ No newline at end of file
+- If the user instructions conflict with best practices, point out the conflict and suggest alternatives
diff --git a/conf/default.php b/conf/default.php
index 1791116..28a3509 100644
--- a/conf/default.php
+++ b/conf/default.php
@@ -37,8 +37,31 @@ $conf['open_service_url'] = 'http://127.0.0.1:8765';
 // Base filesystem path for chronological photo integration.
 $conf['image_base_path'] = '';
 
-// Local calendar ICS files (one absolute file path per line).
-$conf['calendar_ics_files'] = '';
+// Calendar slot configuration (4 slots: general, maintenance, slot3, slot4)
+// Each slot has: file, caldav_url, username, password, color
+$conf['calendar_general_file'] = '';
+$conf['calendar_general_caldav_url'] = '';
+$conf['calendar_general_username'] = '';
+$conf['calendar_general_password'] = '';
+$conf['calendar_general_color'] = '#4a90d9';
+
+$conf['calendar_maintenance_file'] = '';
+$conf['calendar_maintenance_caldav_url'] = '';
+$conf['calendar_maintenance_username'] = '';
+$conf['calendar_maintenance_password'] = '';
+$conf['calendar_maintenance_color'] = '#e67e22';
+
+$conf['calendar_slot3_file'] = '';
+$conf['calendar_slot3_caldav_url'] = '';
+$conf['calendar_slot3_username'] = '';
+$conf['calendar_slot3_password'] = '';
+$conf['calendar_slot3_color'] = '#27ae60';
+
+$conf['calendar_slot4_file'] = '';
+$conf['calendar_slot4_caldav_url'] = '';
+$conf['calendar_slot4_username'] = '';
+$conf['calendar_slot4_password'] = '';
+$conf['calendar_slot4_color'] = '#8e44ad';
 
 // Maximum depth when searching for .pagelink files under allowed roots.
 $conf['pagelink_search_depth'] = 3;
diff --git a/js/event-popup.js b/js/event-popup.js
new file mode 100644
index 0000000..2044c3f
--- /dev/null
+++ b/js/event-popup.js
@@ -0,0 +1,303 @@
+/* global window, document, jQuery */
+
+/**
+ * Event Popup and Maintenance Task Handling
+ *
+ * - Clicking an event item with data-luxtools-event="1" opens a detail popup.
+ * - Clicking a maintenance task action button sends an AJAX request to
+ *   complete/reopen the task.
+ */
+(function () {
+  'use strict';
+
+  var Luxtools = window.Luxtools || (window.Luxtools = {});
+
+  // ============================================================
+  // Event Popup
+  // ============================================================
+  var EventPopup = (function () {
+    var overlay = null;
+    var popup = null;
+
+    function ensureElements() {
+      if (overlay) return;
+
+      overlay = document.createElement('div');
+      overlay.className = 'luxtools-event-popup-overlay';
+      overlay.style.display = 'none';
+
+      popup = document.createElement('div');
+      popup.className = 'luxtools-event-popup';
+      popup.setAttribute('role', 'dialog');
+      popup.setAttribute('aria-modal', 'true');
+
+      overlay.appendChild(popup);
+      document.body.appendChild(overlay);
+
+      overlay.addEventListener('click', function (e) {
+        if (e.target === overlay) {
+          close();
+        }
+      });
+
+      document.addEventListener('keydown', function (e) {
+        if (e.key === 'Escape' && overlay.style.display !== 'none') {
+          close();
+        }
+      });
+    }
+
+    function open(el) {
+      ensureElements();
+
+      var summary = el.getAttribute('data-event-summary') || '';
+      var start = el.getAttribute('data-event-start') || '';
+      var end = el.getAttribute('data-event-end') || '';
+      var location = el.getAttribute('data-event-location') || '';
+      var description = el.getAttribute('data-event-description') || '';
+      var allDay = el.getAttribute('data-event-allday') === '1';
+      var slot = el.getAttribute('data-event-slot') || '';
+
+      var html = '<div class="luxtools-event-popup-content">';
+      html += '<button type="button" class="luxtools-event-popup-close" aria-label="Close">&times;</button>';
+      html += '<h3 class="luxtools-event-popup-title">' + escapeHtml(summary) + '</h3>';
+
+      // Date/time
+      html += '<div class="luxtools-event-popup-field">';
+      if (allDay) {
+        html += '<strong>Date:</strong> ' + formatDate(start);
+        if (end) {
+          html += ' &ndash; ' + formatDate(end);
+        }
+      } else {
+        html += '<strong>Time:</strong> ' + formatDateTime(start);
+        if (end) {
+          html += ' &ndash; ' + formatDateTime(end);
+        }
+      }
+      html += '</div>';
+
+      if (location) {
+        html += '<div class="luxtools-event-popup-field"><strong>Location:</strong> ' + escapeHtml(location) + '</div>';
+      }
+
+      if (description) {
+        html += '<div class="luxtools-event-popup-field luxtools-event-popup-description">'
+          + '<strong>Description:</strong><br>'
+          + escapeHtml(description).replace(/\n/g, '<br>')
+          + '</div>';
+      }
+
+      if (slot) {
+        html += '<div class="luxtools-event-popup-slot"><em>' + escapeHtml(slot) + '</em></div>';
+      }
+
+      html += '</div>';
+
+      popup.innerHTML = html;
+      overlay.style.display = 'flex';
+
+      // Close button inside popup
+      var closeBtn = popup.querySelector('.luxtools-event-popup-close');
+      if (closeBtn) {
+        closeBtn.addEventListener('click', close);
+      }
+    }
+
+    function close() {
+      if (overlay) {
+        overlay.style.display = 'none';
+      }
+    }
+
+    function formatDate(isoStr) {
+      if (!isoStr) return '';
+      var d = new Date(isoStr);
+      if (isNaN(d.getTime())) return isoStr;
+      return d.toLocaleDateString();
+    }
+
+    function formatDateTime(isoStr) {
+      if (!isoStr) return '';
+      var d = new Date(isoStr);
+      if (isNaN(d.getTime())) return isoStr;
+      return d.toLocaleDateString() + ' ' + d.toLocaleTimeString(undefined, { hour: '2-digit', minute: '2-digit' });
+    }
+
+    function escapeHtml(text) {
+      var div = document.createElement('div');
+      div.appendChild(document.createTextNode(text));
+      return div.innerHTML;
+    }
+
+    return {
+      open: open,
+      close: close,
+    };
+  })();
+
+  // ============================================================
+  // Maintenance Task Actions
+  // ============================================================
+  var MaintenanceTasks = (function () {
+
+    function handleAction(button) {
+      var action = button.getAttribute('data-action');
+      if (!action) return;
+
+      // Find the containing list item or container with task data
+      var item = button.closest('[data-task-uid]');
+      if (!item) {
+        // Try the syntax plugin format
+        item = button.closest('[data-uid]');
+      }
+      if (!item) return;
+
+      var uid = item.getAttribute('data-task-uid') || item.getAttribute('data-uid') || '';
+      var date = item.getAttribute('data-task-date') || item.getAttribute('data-date') || '';
+      var recurrence = item.getAttribute('data-task-recurrence') || item.getAttribute('data-recurrence') || '';
+
+      if (!uid || !date) return;
+
+      // Find AJAX URL and security token from parent container or global
+      var container = item.closest('[data-luxtools-ajax-url]');
+      var ajaxUrl = container ? container.getAttribute('data-luxtools-ajax-url') : '';
+      var sectok = container ? container.getAttribute('data-luxtools-sectok') : '';
+
+      if (!ajaxUrl) {
+        // Fallback: use DokuWiki's standard AJAX endpoint
+        ajaxUrl = (window.DOKU_BASE || '/') + 'lib/exe/ajax.php';
+      }
+      if (!sectok && window.JSINFO && window.JSINFO.sectok) {
+        sectok = window.JSINFO.sectok;
+      }
+
+      button.disabled = true;
+      button.textContent = '...';
+
+      var params = 'call=luxtools_maintenance_task'
+        + '&action=' + encodeURIComponent(action)
+        + '&uid=' + encodeURIComponent(uid)
+        + '&date=' + encodeURIComponent(date)
+        + '&recurrence=' + encodeURIComponent(recurrence)
+        + '&sectok=' + encodeURIComponent(sectok);
+
+      var xhr = new XMLHttpRequest();
+      xhr.open('POST', ajaxUrl, true);
+      xhr.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
+
+      xhr.onload = function () {
+        var result;
+        try {
+          result = JSON.parse(xhr.responseText);
+        } catch (e) {
+          result = { ok: false, error: 'Invalid response' };
+        }
+
+        if (result.ok) {
+          // Visual feedback: mark item as done or revert
+          if (action === 'complete') {
+            item.classList.add('luxtools-task-completed');
+            // Fade out and remove after a short delay
+            item.style.opacity = '0.5';
+            setTimeout(function () {
+              item.style.display = 'none';
+            }, 1000);
+          } else {
+            item.classList.remove('luxtools-task-completed');
+            item.style.opacity = '1';
+            button.textContent = 'Complete';
+            button.setAttribute('data-action', 'complete');
+            button.disabled = false;
+          }
+
+          // Show remote write warning if applicable
+          if (result.remoteOk === false && result.remoteError) {
+            showNotification(result.remoteError, 'warning');
+          }
+        } else {
+          var errMsg = result.error || 'Action failed';
+          showNotification(errMsg, 'error');
+          button.textContent = action === 'complete' ? 'Complete' : 'Reopen';
+          button.disabled = false;
+        }
+      };
+
+      xhr.onerror = function () {
+        showNotification('Network error', 'error');
+        button.textContent = action === 'complete' ? 'Complete' : 'Reopen';
+        button.disabled = false;
+      };
+
+      xhr.send(params);
+    }
+
+    function showNotification(message, type) {
+      // Use DokuWiki msg() if available
+      if (typeof window.msg === 'function') {
+        var level = (type === 'error') ? -1 : ((type === 'warning') ? 0 : 1);
+        window.msg(message, level);
+        return;
+      }
+
+      // Fallback: simple notification
+      var notif = document.createElement('div');
+      notif.className = 'luxtools-notification luxtools-notification-' + type;
+      notif.textContent = message;
+      document.body.appendChild(notif);
+      setTimeout(function () {
+        if (notif.parentNode) notif.parentNode.removeChild(notif);
+      }, 5000);
+    }
+
+    return {
+      handleAction: handleAction,
+    };
+  })();
+
+  // ============================================================
+  // Event Delegation
+  // ============================================================
+  document.addEventListener('click', function (e) {
+    var target = e.target;
+
+    // Maintenance task action buttons (day pages)
+    if (target.classList && target.classList.contains('luxtools-task-action')) {
+      e.preventDefault();
+      MaintenanceTasks.handleAction(target);
+      return;
+    }
+
+    // Maintenance task complete buttons (syntax plugin list)
+    if (target.classList && target.classList.contains('luxtools-task-complete-btn')) {
+      e.preventDefault();
+      MaintenanceTasks.handleAction(target);
+      return;
+    }
+
+    // Event popup: find closest element with data-luxtools-event
+    var eventEl = target.closest ? target.closest('[data-luxtools-event]') : null;
+    if (!eventEl) {
+      // Traverse manually for older browsers
+      var el = target;
+      while (el && el !== document) {
+        if (el.getAttribute && el.getAttribute('data-luxtools-event') === '1') {
+          eventEl = el;
+          break;
+        }
+        el = el.parentNode;
+      }
+    }
+
+    if (eventEl) {
+      // Don't open popup if clicking a button inside the event item
+      if (target.tagName === 'BUTTON' || target.closest('button')) return;
+
+      e.preventDefault();
+      EventPopup.open(eventEl);
+    }
+  }, false);
+
+  Luxtools.EventPopup = EventPopup;
+  Luxtools.MaintenanceTasks = MaintenanceTasks;
+})();
diff --git a/lang/de/lang.php b/lang/de/lang.php
index a650a9d..cffa425 100644
--- a/lang/de/lang.php
+++ b/lang/de/lang.php
@@ -64,8 +64,12 @@ $lang["open_service_url"] =
     "URL des lokalen Client-Dienstes für {{open>...}} (z.B. http://127.0.0.1:8765).";
 $lang["image_base_path"] =
     "Basis-Dateisystempfad für die chronologische Foto-Integration.";
-$lang["calendar_ics_files"] =
-    "Lokale Kalender-.ics-Dateien (ein absoluter Dateipfad pro Zeile).";
+$lang["calendar_slot_heading"] = "Kalender-Slot";
+$lang["calendar_slot_file"] = "Lokaler ICS-Dateipfad";
+$lang["calendar_slot_caldav_url"] = "CalDAV-URL";
+$lang["calendar_slot_username"] = "Benutzername";
+$lang["calendar_slot_password"] = "Passwort";
+$lang["calendar_slot_color"] = "Anzeigefarbe";
 $lang["pagelink_search_depth"] =
     "Maximale Verzeichnisebene für .pagelink-Suche (0 = nur Root).";
 
@@ -85,6 +89,18 @@ $lang["pagelink_unlinked"] = "Seite nicht verknüpft";
 $lang["pagelink_multi_warning"] = "Mehrere Ordner verknüpft";
 $lang["chronological_photos_title"] = "Fotos";
 $lang["chronological_events_title"] = "Termine";
+$lang["chronological_maintenance_title"] = "Aufgaben";
+$lang["maintenance_task_complete"] = "Erledigen";
+$lang["maintenance_task_reopen"] = "Wieder öffnen";
+$lang["maintenance_no_tasks"] = "Keine offenen Aufgaben.";
+$lang["maintenance_complete_success"] = "Aufgabe als erledigt markiert.";
+$lang["maintenance_complete_error"] = "Aktualisierung der Aufgabe fehlgeschlagen.";
+$lang["maintenance_reopen_success"] = "Aufgabe wieder geöffnet.";
+$lang["maintenance_remote_write_failed"] = "Lokale Aktualisierung erfolgreich, aber CalDAV-Update fehlgeschlagen. Wird bei nächster Synchronisierung erneut versucht.";
+$lang["calendar_sync_button"] = "Kalender synchronisieren";
+$lang["calendar_sync_success"] = "Kalender-Synchronisierung abgeschlossen.";
+$lang["calendar_sync_error"] = "Kalender-Synchronisierung fehlgeschlagen.";
+$lang["calendar_sync_partial"] = "Kalender-Synchronisierung mit Fehlern abgeschlossen.";
 $lang["cache_invalidate_button"] = "Cache invalidieren";
 $lang["cache_invalidate_button_title"] = "Gesamten DokuWiki-Cache leeren";
 $lang["cache_invalidate_success"] = "DokuWiki-Cache invalidiert.";
diff --git a/lang/en/lang.php b/lang/en/lang.php
index 2acc214..887e620 100644
--- a/lang/en/lang.php
+++ b/lang/en/lang.php
@@ -64,8 +64,12 @@ $lang["open_service_url"] =
     "Local client service URL for the {{open>...}} button (e.g. http://127.0.0.1:8765).";
 $lang["image_base_path"] =
     "Base filesystem path for chronological photo integration.";
-$lang["calendar_ics_files"] =
-    "Local calendar .ics files (one absolute file path per line).";
+$lang["calendar_slot_heading"] = "Calendar Slot";
+$lang["calendar_slot_file"] = "Local ICS file path";
+$lang["calendar_slot_caldav_url"] = "CalDAV URL";
+$lang["calendar_slot_username"] = "Username";
+$lang["calendar_slot_password"] = "Password";
+$lang["calendar_slot_color"] = "Display color";
 $lang["pagelink_search_depth"] =
     "Maximum directory depth for .pagelink search (0 = only root).";
 
@@ -86,6 +90,18 @@ $lang["pagelink_multi_warning"] = "Multiple folders linked";
 $lang["calendar_err_badmonth"] = "Invalid calendar month. Use YYYY-MM.";
 $lang["chronological_photos_title"] = "Photos";
 $lang["chronological_events_title"] = "Events";
+$lang["chronological_maintenance_title"] = "Tasks";
+$lang["maintenance_task_complete"] = "Complete";
+$lang["maintenance_task_reopen"] = "Reopen";
+$lang["maintenance_no_tasks"] = "No open tasks.";
+$lang["maintenance_complete_success"] = "Task marked as completed.";
+$lang["maintenance_complete_error"] = "Failed to update task.";
+$lang["maintenance_reopen_success"] = "Task reopened.";
+$lang["maintenance_remote_write_failed"] = "Local update succeeded, but remote CalDAV update failed. Will retry on next sync.";
+$lang["calendar_sync_button"] = "Sync Calendars";
+$lang["calendar_sync_success"] = "Calendar sync completed.";
+$lang["calendar_sync_error"] = "Calendar sync failed.";
+$lang["calendar_sync_partial"] = "Calendar sync completed with errors.";
 $lang["cache_invalidate_button"] = "Invalidate Cache";
 $lang["cache_invalidate_button_title"] = "Purge the entire DokuWiki cache";
 $lang["cache_invalidate_success"] = "DokuWiki cache invalidated.";
diff --git a/src/CalDavClient.php b/src/CalDavClient.php
new file mode 100644
index 0000000..e4c0ef4
--- /dev/null
+++ b/src/CalDavClient.php
@@ -0,0 +1,466 @@
+<?php
+
+namespace dokuwiki\plugin\luxtools;
+
+use Sabre\VObject\Component\VCalendar;
+use Sabre\VObject\Reader;
+use Throwable;
+
+/**
+ * CalDAV client for remote calendar operations.
+ *
+ * Supports:
+ * - Downloading a full calendar collection into a local ICS file (sync)
+ * - Updating the STATUS of a single event/task occurrence on the remote server
+ *
+ * Uses plain PHP curl for HTTP. No additional dependencies required.
+ */
+class CalDavClient
+{
+    /** @var int HTTP timeout in seconds */
+    protected const TIMEOUT = 30;
+
+    /**
+     * Update the STATUS of a specific event or task on the remote CalDAV server.
+     *
+     * Fetches the calendar object containing the UID, modifies its status,
+     * and PUTs it back using the ETag for conflict detection.
+     *
+     * @param string $caldavUrl  CalDAV collection URL
+     * @param string $username   HTTP Basic auth username
+     * @param string $password   HTTP Basic auth password
+     * @param string $uid        Event/task UID
+     * @param string $recurrenceId  Recurrence ID (empty for non-recurring)
+     * @param string $newStatus  New status value (e.g. COMPLETED, TODO)
+     * @param string $dateIso    Occurrence date YYYY-MM-DD
+     * @return bool  True if the remote update succeeded
+     */
+    public static function updateEventStatus(
+        string $caldavUrl,
+        string $username,
+        string $password,
+        string $uid,
+        string $recurrenceId,
+        string $newStatus,
+        string $dateIso
+    ): bool {
+        if ($caldavUrl === '' || $uid === '') return false;
+
+        try {
+            // Find the calendar object href for this UID via REPORT
+            $objectInfo = self::findObjectByUid($caldavUrl, $username, $password, $uid);
+            if ($objectInfo === null) return false;
+
+            $objectHref = $objectInfo['href'];
+            $etag = $objectInfo['etag'];
+            $calendarData = $objectInfo['data'];
+
+            // Parse and update the status
+            $calendar = Reader::read($calendarData, Reader::OPTION_FORGIVING);
+            if (!($calendar instanceof VCalendar)) return false;
+
+            $updated = IcsWriter::applyStatusUpdateToCalendar(
+                $calendar, $uid, $recurrenceId, $newStatus, $dateIso
+            );
+            if (!$updated) return false;
+
+            $newData = $calendar->serialize();
+
+            // PUT the updated object back with If-Match for conflict detection
+            return self::putCalendarObject($objectHref, $username, $password, $newData, $etag);
+        } catch (Throwable $e) {
+            return false;
+        }
+    }
+
+    /**
+     * Sync a remote CalDAV calendar collection into the slot's local ICS file.
+     *
+     * Downloads all calendar objects from the collection and merges them
+     * into a single ICS file at the slot's configured file path.
+     *
+     * @param CalendarSlot $slot
+     * @return bool  True if sync succeeded
+     */
+    public static function syncSlot(CalendarSlot $slot): bool
+    {
+        if (!$slot->hasRemoteSource()) return false;
+
+        $caldavUrl = $slot->getCaldavUrl();
+        $username = $slot->getUsername();
+        $password = $slot->getPassword();
+        $localFile = $slot->getFile();
+
+        if ($localFile === '') {
+            // No local file configured - nothing to sync into
+            return false;
+        }
+
+        try {
+            $objects = self::fetchAllCalendarObjects($caldavUrl, $username, $password);
+            if ($objects === null) return false;
+
+            $merged = self::mergeCalendarObjects($objects);
+            if ($merged === '') return false;
+
+            return IcsWriter::atomicWritePublic($localFile, $merged);
+        } catch (Throwable $e) {
+            return false;
+        }
+    }
+
+    /**
+     * Find a specific calendar object by UID using a REPORT request.
+     *
+     * @param string $caldavUrl
+     * @param string $username
+     * @param string $password
+     * @param string $uid
+     * @return array{href: string, etag: string, data: string}|null
+     */
+    protected static function findObjectByUid(
+        string $caldavUrl,
+        string $username,
+        string $password,
+        string $uid
+    ): ?array {
+        $body = '<?xml version="1.0" encoding="utf-8" ?>' .
+            '<C:calendar-query xmlns:D="DAV:" xmlns:C="urn:ietf:params:xml:ns:caldav">' .
+            '<D:prop>' .
+            '<D:getetag/>' .
+            '<C:calendar-data/>' .
+            '</D:prop>' .
+            '<C:filter>' .
+            '<C:comp-filter name="VCALENDAR">' .
+            '<C:comp-filter name="VEVENT">' .
+            '<C:prop-filter name="UID">' .
+            '<C:text-match collation="i;octet">' . htmlspecialchars($uid, ENT_XML1, 'UTF-8') . '</C:text-match>' .
+            '</C:prop-filter>' .
+            '</C:comp-filter>' .
+            '</C:comp-filter>' .
+            '</C:filter>' .
+            '</C:calendar-query>';
+
+        $response = self::request('REPORT', $caldavUrl, $username, $password, $body, [
+            'Content-Type: application/xml; charset=utf-8',
+            'Depth: 1',
+        ]);
+
+        if ($response === null) {
+            // Try VTODO filter as well
+            $body = '<?xml version="1.0" encoding="utf-8" ?>' .
+                '<C:calendar-query xmlns:D="DAV:" xmlns:C="urn:ietf:params:xml:ns:caldav">' .
+                '<D:prop>' .
+                '<D:getetag/>' .
+                '<C:calendar-data/>' .
+                '</D:prop>' .
+                '<C:filter>' .
+                '<C:comp-filter name="VCALENDAR">' .
+                '<C:comp-filter name="VTODO">' .
+                '<C:prop-filter name="UID">' .
+                '<C:text-match collation="i;octet">' . htmlspecialchars($uid, ENT_XML1, 'UTF-8') . '</C:text-match>' .
+                '</C:prop-filter>' .
+                '</C:comp-filter>' .
+                '</C:comp-filter>' .
+                '</C:filter>' .
+                '</C:calendar-query>';
+
+            $response = self::request('REPORT', $caldavUrl, $username, $password, $body, [
+                'Content-Type: application/xml; charset=utf-8',
+                'Depth: 1',
+            ]);
+        }
+
+        if ($response === null) return null;
+
+        return self::parseReportResponse($response, $caldavUrl);
+    }
+
+    /**
+     * Fetch all calendar objects from a CalDAV collection.
+     *
+     * @param string $caldavUrl
+     * @param string $username
+     * @param string $password
+     * @return string[]|null  Array of ICS data strings, or null on failure
+     */
+    protected static function fetchAllCalendarObjects(
+        string $caldavUrl,
+        string $username,
+        string $password
+    ): ?array {
+        $body = '<?xml version="1.0" encoding="utf-8" ?>' .
+            '<C:calendar-query xmlns:D="DAV:" xmlns:C="urn:ietf:params:xml:ns:caldav">' .
+            '<D:prop>' .
+            '<C:calendar-data/>' .
+            '</D:prop>' .
+            '<C:filter>' .
+            '<C:comp-filter name="VCALENDAR"/>' .
+            '</C:filter>' .
+            '</C:calendar-query>';
+
+        $response = self::request('REPORT', $caldavUrl, $username, $password, $body, [
+            'Content-Type: application/xml; charset=utf-8',
+            'Depth: 1',
+        ]);
+
+        if ($response === null) return null;
+
+        return self::parseCalendarDataFromMultistatus($response);
+    }
+
+    /**
+     * Merge multiple ICS calendar objects into a single calendar string.
+     *
+     * @param string[] $objects  Array of ICS data strings
+     * @return string  Merged ICS content
+     */
+    protected static function mergeCalendarObjects(array $objects): string
+    {
+        if ($objects === []) return '';
+
+        $merged = new VCalendar();
+        $merged->PRODID = '-//LuxTools DokuWiki Plugin//CalDAV Sync//EN';
+        $merged->VERSION = '2.0';
+
+        foreach ($objects as $icsData) {
+            if (trim($icsData) === '') continue;
+            try {
+                $cal = Reader::read($icsData, Reader::OPTION_FORGIVING);
+                if (!($cal instanceof VCalendar)) continue;
+
+                // Copy VTIMEZONE components first
+                foreach ($cal->select('VTIMEZONE') as $tz) {
+                    // Check if this timezone already exists in merged
+                    $tzid = (string)($tz->TZID ?? '');
+                    $exists = false;
+                    foreach ($merged->select('VTIMEZONE') as $existingTz) {
+                        if ((string)($existingTz->TZID ?? '') === $tzid) {
+                            $exists = true;
+                            break;
+                        }
+                    }
+                    if (!$exists) {
+                        $merged->add(clone $tz);
+                    }
+                }
+
+                // Copy VEVENT and VTODO components
+                foreach ($cal->select('VEVENT') as $component) {
+                    $merged->add(clone $component);
+                }
+                foreach ($cal->select('VTODO') as $component) {
+                    $merged->add(clone $component);
+                }
+            } catch (Throwable $e) {
+                // Skip malformed objects
+                continue;
+            }
+        }
+
+        return $merged->serialize();
+    }
+
+    /**
+     * PUT a calendar object back to the server.
+     *
+     * @param string $href     Full URL of the calendar object
+     * @param string $username
+     * @param string $password
+     * @param string $data     ICS data to write
+     * @param string $etag     ETag for If-Match header (empty to skip)
+     * @return bool
+     */
+    protected static function putCalendarObject(
+        string $href,
+        string $username,
+        string $password,
+        string $data,
+        string $etag
+    ): bool {
+        $headers = [
+            'Content-Type: text/calendar; charset=utf-8',
+        ];
+        if ($etag !== '') {
+            $headers[] = 'If-Match: ' . $etag;
+        }
+
+        $response = self::request('PUT', $href, $username, $password, $data, $headers);
+        // PUT returns null body but we check by HTTP status via the request method
+        // A successful PUT returns 2xx
+        return $response !== null;
+    }
+
+    /**
+     * Parse a REPORT multistatus response to extract href, etag, and calendar data
+     * for the first matching object.
+     *
+     * @param string $xml
+     * @param string $baseUrl
+     * @return array{href: string, etag: string, data: string}|null
+     */
+    protected static function parseReportResponse(string $xml, string $baseUrl): ?array
+    {
+        $doc = self::parseXml($xml);
+        if ($doc === null) return null;
+
+        $doc->registerXPathNamespace('d', 'DAV:');
+        $doc->registerXPathNamespace('cal', 'urn:ietf:params:xml:ns:caldav');
+
+        $responses = $doc->xpath('//d:response');
+        if (!$responses || count($responses) === 0) return null;
+
+        foreach ($responses as $resp) {
+            $resp->registerXPathNamespace('d', 'DAV:');
+            $resp->registerXPathNamespace('cal', 'urn:ietf:params:xml:ns:caldav');
+
+            $hrefs = $resp->xpath('d:href');
+            $href = ($hrefs && count($hrefs) > 0) ? trim((string)$hrefs[0]) : '';
+
+            $etags = $resp->xpath('.//d:getetag');
+            $etag = ($etags && count($etags) > 0) ? trim((string)$etags[0]) : '';
+            // Strip surrounding quotes from etag if present
+            $etag = trim($etag, '"');
+
+            $caldata = $resp->xpath('.//cal:calendar-data');
+            $data = ($caldata && count($caldata) > 0) ? trim((string)$caldata[0]) : '';
+
+            if ($href === '' || $data === '') continue;
+
+            // Resolve relative href to absolute URL
+            if (strpos($href, 'http') !== 0) {
+                $parsed = parse_url($baseUrl);
+                $scheme = ($parsed['scheme'] ?? 'https');
+                $host = ($parsed['host'] ?? '');
+                $port = isset($parsed['port']) ? (':' . $parsed['port']) : '';
+                $href = $scheme . '://' . $host . $port . $href;
+            }
+
+            return [
+                'href' => $href,
+                'etag' => $etag,
+                'data' => $data,
+            ];
+        }
+
+        return null;
+    }
+
+    /**
+     * Parse calendar-data elements from a CalDAV multistatus response.
+     *
+     * @param string $xml
+     * @return string[]
+     */
+    protected static function parseCalendarDataFromMultistatus(string $xml): array
+    {
+        $doc = self::parseXml($xml);
+        if ($doc === null) return [];
+
+        $doc->registerXPathNamespace('d', 'DAV:');
+        $doc->registerXPathNamespace('cal', 'urn:ietf:params:xml:ns:caldav');
+
+        $results = [];
+        $responses = $doc->xpath('//d:response');
+        if (!$responses) return [];
+
+        foreach ($responses as $resp) {
+            $resp->registerXPathNamespace('cal', 'urn:ietf:params:xml:ns:caldav');
+            $caldata = $resp->xpath('.//cal:calendar-data');
+            if ($caldata && count($caldata) > 0) {
+                $data = trim((string)$caldata[0]);
+                if ($data !== '') {
+                    $results[] = $data;
+                }
+            }
+        }
+
+        return $results;
+    }
+
+    /**
+     * Parse an XML string safely.
+     *
+     * @param string $xml
+     * @return \SimpleXMLElement|null
+     */
+    protected static function parseXml(string $xml): ?\SimpleXMLElement
+    {
+        if (trim($xml) === '') return null;
+
+        // Disable external entity loading for security
+        $prev = libxml_use_internal_errors(true);
+        try {
+            $doc = simplexml_load_string($xml, 'SimpleXMLElement', LIBXML_NOENT | LIBXML_NONET);
+            libxml_clear_errors();
+            return ($doc !== false) ? $doc : null;
+        } finally {
+            libxml_use_internal_errors($prev);
+        }
+    }
+
+    /**
+     * Perform an HTTP request to a CalDAV server.
+     *
+     * @param string $method   HTTP method (GET, PUT, REPORT, PROPFIND, etc.)
+     * @param string $url      Full URL
+     * @param string $username
+     * @param string $password
+     * @param string $body     Request body (empty for GET)
+     * @param string[] $headers Additional HTTP headers
+     * @return string|null  Response body, or null on failure
+     */
+    protected static function request(
+        string $method,
+        string $url,
+        string $username,
+        string $password,
+        string $body = '',
+        array $headers = []
+    ): ?string {
+        if (!function_exists('curl_init')) return null;
+
+        $ch = curl_init();
+        if ($ch === false) return null;
+
+        curl_setopt($ch, CURLOPT_URL, $url);
+        curl_setopt($ch, CURLOPT_CUSTOMREQUEST, $method);
+        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
+        curl_setopt($ch, CURLOPT_TIMEOUT, self::TIMEOUT);
+        curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
+        curl_setopt($ch, CURLOPT_MAXREDIRS, 5);
+
+        // Authentication
+        if ($username !== '') {
+            curl_setopt($ch, CURLOPT_HTTPAUTH, CURLAUTH_BASIC);
+            curl_setopt($ch, CURLOPT_USERPWD, $username . ':' . $password);
+        }
+
+        // Request body
+        if ($body !== '') {
+            curl_setopt($ch, CURLOPT_POSTFIELDS, $body);
+        }
+
+        // HTTP headers
+        if ($headers !== []) {
+            curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
+        }
+
+        // Capture HTTP status code
+        $responseBody = curl_exec($ch);
+        $httpCode = (int)curl_getinfo($ch, CURLINFO_HTTP_CODE);
+        curl_close($ch);
+
+        if (!is_string($responseBody)) return null;
+
+        // Accept 2xx and 207 (multistatus) responses
+        if ($httpCode >= 200 && $httpCode < 300) {
+            return $responseBody;
+        }
+        if ($httpCode === 207) {
+            return $responseBody;
+        }
+
+        return null;
+    }
+}
diff --git a/src/CalendarEvent.php b/src/CalendarEvent.php
new file mode 100644
index 0000000..a0e222c
--- /dev/null
+++ b/src/CalendarEvent.php
@@ -0,0 +1,86 @@
+<?php
+
+namespace dokuwiki\plugin\luxtools;
+
+/**
+ * Normalized calendar event/task for internal use.
+ *
+ * All calendar data (from any slot, any source) is converted into this
+ * structure before rendering or querying.
+ */
+class CalendarEvent
+{
+    /** @var string Calendar slot key (e.g. 'general', 'maintenance') */
+    public $slotKey;
+
+    /** @var string Unique source event UID */
+    public $uid;
+
+    /** @var string Recurrence ID (empty for non-recurring or master) */
+    public $recurrenceId;
+
+    /** @var string Event summary/title */
+    public $summary;
+
+    /** @var string ISO 8601 start date/time */
+    public $startIso;
+
+    /** @var string ISO 8601 end date/time (may be empty) */
+    public $endIso;
+
+    /** @var bool Whether this is an all-day event */
+    public $allDay;
+
+    /** @var string Formatted time string (HH:MM) or empty for all-day */
+    public $time;
+
+    /** @var string Location (may be empty) */
+    public $location;
+
+    /** @var string Description (may be empty) */
+    public $description;
+
+    /**
+     * Status: empty, CONFIRMED, TENTATIVE, CANCELLED, TODO, COMPLETED,
+     * IN-PROCESS, NEEDS-ACTION.
+     * @var string
+     */
+    public $status;
+
+    /** @var string Component type from source: VEVENT or VTODO */
+    public $componentType;
+
+    /** @var string The date (YYYY-MM-DD) this event applies to */
+    public $dateIso;
+
+    /**
+     * Build a stable completion key for maintenance task tracking.
+     *
+     * @return string
+     */
+    public function completionKey(): string
+    {
+        return implode('|', [$this->slotKey, $this->uid, $this->dateIso]);
+    }
+
+    /**
+     * Whether this event/task is marked as completed.
+     *
+     * @return bool
+     */
+    public function isCompleted(): bool
+    {
+        $s = strtoupper($this->status);
+        return $s === 'COMPLETED';
+    }
+
+    /**
+     * Whether this event/task is open (for maintenance filtering).
+     *
+     * @return bool
+     */
+    public function isOpen(): bool
+    {
+        return !$this->isCompleted();
+    }
+}
diff --git a/src/CalendarService.php b/src/CalendarService.php
new file mode 100644
index 0000000..b2c892d
--- /dev/null
+++ b/src/CalendarService.php
@@ -0,0 +1,553 @@
+<?php
+
+namespace dokuwiki\plugin\luxtools;
+
+use DateInterval;
+use DateTimeImmutable;
+use DateTimeInterface;
+use DateTimeZone;
+use Sabre\VObject\Component\VCalendar;
+use Sabre\VObject\Component\VEvent;
+use Sabre\VObject\Component\VTodo;
+use Sabre\VObject\Reader;
+use Throwable;
+
+/**
+ * Slot-aware calendar service.
+ *
+ * Provides normalized event data grouped by slot for rendering,
+ * widget indicators, task list queries, and completion tracking.
+ */
+class CalendarService
+{
+    /** @var array<string,CalendarEvent[]> In-request cache keyed by "slotKey|dateIso" */
+    protected static $dayCache = [];
+
+    /** @var array<string,CalendarEvent[]> In-request cache keyed by "slotKey|all" for open tasks */
+    protected static $taskCache = [];
+
+    /**
+     * Get all normalized events for a given date across all enabled slots.
+     *
+     * @param CalendarSlot[] $slots Keyed by slot key
+     * @param string $dateIso YYYY-MM-DD
+     * @return CalendarEvent[] Sorted: all-day first, then by time, then by title
+     */
+    public static function eventsForDate(array $slots, string $dateIso): array
+    {
+        if (!ChronoID::isIsoDate($dateIso)) return [];
+
+        $all = [];
+        foreach ($slots as $slot) {
+            if (!$slot->isEnabled()) continue;
+            $events = self::slotEventsForDate($slot, $dateIso);
+            foreach ($events as $event) {
+                $all[] = $event;
+            }
+        }
+
+        usort($all, [self::class, 'compareEvents']);
+        return $all;
+    }
+
+    /**
+     * Get events for a specific slot and date.
+     *
+     * @param CalendarSlot $slot
+     * @param string $dateIso
+     * @return CalendarEvent[]
+     */
+    public static function slotEventsForDate(CalendarSlot $slot, string $dateIso): array
+    {
+        if (!ChronoID::isIsoDate($dateIso)) return [];
+        if (!$slot->isEnabled()) return [];
+
+        $cacheKey = $slot->getKey() . '|' . $dateIso;
+        if (isset(self::$dayCache[$cacheKey])) {
+            return self::$dayCache[$cacheKey];
+        }
+
+        $events = [];
+        $file = $slot->getFile();
+        if ($file !== '' && is_file($file) && is_readable($file)) {
+            $events = self::parseEventsFromFile($file, $slot->getKey(), $dateIso);
+        }
+
+        self::$dayCache[$cacheKey] = $events;
+        return $events;
+    }
+
+    /**
+     * Get events for a specific slot on a date, grouped by slot key.
+     *
+     * @param CalendarSlot[] $slots
+     * @param string $dateIso
+     * @return array<string,CalendarEvent[]> Keyed by slot key
+     */
+    public static function eventsForDateGrouped(array $slots, string $dateIso): array
+    {
+        $grouped = [];
+        foreach ($slots as $slot) {
+            if (!$slot->isEnabled()) continue;
+            $events = self::slotEventsForDate($slot, $dateIso);
+            if ($events !== []) {
+                $grouped[$slot->getKey()] = $events;
+            }
+        }
+        return $grouped;
+    }
+
+    /**
+     * Check whether a slot has any events on a given date.
+     *
+     * @param CalendarSlot $slot
+     * @param string $dateIso
+     * @return bool
+     */
+    public static function slotHasEventsOnDate(CalendarSlot $slot, string $dateIso): bool
+    {
+        return self::slotEventsForDate($slot, $dateIso) !== [];
+    }
+
+    /**
+     * Get all open maintenance tasks due up to (and including) today.
+     *
+     * @param CalendarSlot $maintenanceSlot
+     * @param string $todayIso YYYY-MM-DD
+     * @return CalendarEvent[] Sorted: overdue first, then today, then by title
+     */
+    public static function openMaintenanceTasks(CalendarSlot $maintenanceSlot, string $todayIso): array
+    {
+        if (!$maintenanceSlot->isEnabled()) return [];
+        if (!ChronoID::isIsoDate($todayIso)) return [];
+
+        $file = $maintenanceSlot->getFile();
+        if ($file === '' || !is_file($file) || !is_readable($file)) return [];
+
+        $cacheKey = $maintenanceSlot->getKey() . '|tasks|' . $todayIso;
+        if (isset(self::$taskCache[$cacheKey])) {
+            return self::$taskCache[$cacheKey];
+        }
+
+        $tasks = self::parseAllTasksFromFile($file, $maintenanceSlot->getKey(), $todayIso);
+
+        // Filter: only non-completed, due today or earlier
+        $open = [];
+        foreach ($tasks as $task) {
+            if ($task->isCompleted()) continue;
+            // dateIso is the date the task falls on
+            if ($task->dateIso > $todayIso) continue;
+            $open[] = $task;
+        }
+
+        // Sort: overdue first, then today, then by time, then by title
+        usort($open, static function (CalendarEvent $a, CalendarEvent $b) use ($todayIso): int {
+            $aOverdue = $a->dateIso < $todayIso;
+            $bOverdue = $b->dateIso < $todayIso;
+            if ($aOverdue !== $bOverdue) {
+                return $aOverdue ? -1 : 1;
+            }
+            $dateCmp = strcmp($a->dateIso, $b->dateIso);
+            if ($dateCmp !== 0) return $dateCmp;
+
+            $timeCmp = strcmp($a->time, $b->time);
+            if ($timeCmp !== 0) return $timeCmp;
+
+            return strcmp($a->summary, $b->summary);
+        });
+
+        self::$taskCache[$cacheKey] = $open;
+        return $open;
+    }
+
+    /**
+     * Get slot-level day indicator data for a whole month.
+     *
+     * @param CalendarSlot[] $slots
+     * @param int $year
+     * @param int $month
+     * @return array<string,string[]> date => [slotKey, ...]
+     */
+    public static function monthIndicators(array $slots, int $year, int $month): array
+    {
+        $daysInMonth = (int)date('t', mktime(0, 0, 0, $month, 1, $year));
+        $indicators = [];
+
+        foreach ($slots as $slot) {
+            if (!$slot->isEnabled()) continue;
+            for ($day = 1; $day <= $daysInMonth; $day++) {
+                $dateIso = sprintf('%04d-%02d-%02d', $year, $month, $day);
+                if (self::slotHasEventsOnDate($slot, $dateIso)) {
+                    $indicators[$dateIso][] = $slot->getKey();
+                }
+            }
+        }
+
+        return $indicators;
+    }
+
+    /**
+     * Parse events from a local ICS file for a specific date.
+     *
+     * @param string $file
+     * @param string $slotKey
+     * @param string $dateIso
+     * @return CalendarEvent[]
+     */
+    protected static function parseEventsFromFile(string $file, string $slotKey, string $dateIso): array
+    {
+        $raw = @file_get_contents($file);
+        if (!is_string($raw) || trim($raw) === '') return [];
+
+        try {
+            $component = Reader::read($raw, Reader::OPTION_FORGIVING);
+            if (!($component instanceof VCalendar)) return [];
+
+            $utc = new DateTimeZone('UTC');
+            $rangeStart = new DateTimeImmutable($dateIso . ' 00:00:00', $utc);
+            $rangeStart = $rangeStart->sub(new DateInterval('P1D'));
+            $rangeEnd = $rangeStart->add(new DateInterval('P3D'));
+
+            $expanded = $component->expand($rangeStart, $rangeEnd);
+            if (!($expanded instanceof VCalendar)) return [];
+
+            return self::collectFromCalendar($expanded, $slotKey, $dateIso);
+        } catch (Throwable $e) {
+            return [];
+        }
+    }
+
+    /**
+     * Parse all tasks (VEVENT with STATUS or VTODO) from a maintenance file,
+     * expanding recurrences up to the given date.
+     *
+     * @param string $file
+     * @param string $slotKey
+     * @param string $todayIso
+     * @return CalendarEvent[]
+     */
+    protected static function parseAllTasksFromFile(string $file, string $slotKey, string $todayIso): array
+    {
+        $raw = @file_get_contents($file);
+        if (!is_string($raw) || trim($raw) === '') return [];
+
+        try {
+            $component = Reader::read($raw, Reader::OPTION_FORGIVING);
+            if (!($component instanceof VCalendar)) return [];
+
+            // Expand from a reasonable lookback to tomorrow
+            $utc = new DateTimeZone('UTC');
+            $rangeStart = new DateTimeImmutable('2020-01-01 00:00:00', $utc);
+            $rangeEnd = new DateTimeImmutable($todayIso . ' 00:00:00', $utc);
+            $rangeEnd = $rangeEnd->add(new DateInterval('P1D'));
+
+            $expanded = $component->expand($rangeStart, $rangeEnd);
+            if (!($expanded instanceof VCalendar)) return [];
+
+            $tasks = [];
+
+            // Collect VEVENTs
+            foreach ($expanded->select('VEVENT') as $vevent) {
+                if (!($vevent instanceof VEvent)) continue;
+                $event = self::normalizeVEvent($vevent, $slotKey);
+                if ($event !== null) {
+                    $tasks[] = $event;
+                }
+            }
+
+            // Collect VTODOs
+            foreach ($expanded->select('VTODO') as $vtodo) {
+                if (!($vtodo instanceof VTodo)) continue;
+                $event = self::normalizeVTodo($vtodo, $slotKey);
+                if ($event !== null) {
+                    $tasks[] = $event;
+                }
+            }
+
+            return $tasks;
+        } catch (Throwable $e) {
+            return [];
+        }
+    }
+
+    /**
+     * Collect normalized events from an expanded VCalendar for a specific date.
+     *
+     * @param VCalendar $calendar
+     * @param string $slotKey
+     * @param string $dateIso
+     * @return CalendarEvent[]
+     */
+    protected static function collectFromCalendar(VCalendar $calendar, string $slotKey, string $dateIso): array
+    {
+        $result = [];
+        $seen = [];
+
+        // VEVENTs
+        foreach ($calendar->select('VEVENT') as $vevent) {
+            if (!($vevent instanceof VEvent)) continue;
+            $event = self::normalizeVEventForDay($vevent, $slotKey, $dateIso);
+            if ($event === null) continue;
+
+            $dedupeKey = $event->uid . '|' . $event->recurrenceId . '|' . $event->startIso . '|' . $event->summary;
+            if (isset($seen[$dedupeKey])) continue;
+            $seen[$dedupeKey] = true;
+            $result[] = $event;
+        }
+
+        // VTODOs
+        foreach ($calendar->select('VTODO') as $vtodo) {
+            if (!($vtodo instanceof VTodo)) continue;
+            $event = self::normalizeVTodoForDay($vtodo, $slotKey, $dateIso);
+            if ($event === null) continue;
+
+            $dedupeKey = $event->uid . '|' . $event->recurrenceId . '|' . $event->startIso . '|' . $event->summary;
+            if (isset($seen[$dedupeKey])) continue;
+            $seen[$dedupeKey] = true;
+            $result[] = $event;
+        }
+
+        usort($result, [self::class, 'compareEvents']);
+        return $result;
+    }
+
+    /**
+     * Normalize a VEVENT for a specific day into a CalendarEvent.
+     *
+     * @param VEvent $vevent
+     * @param string $slotKey
+     * @param string $dateIso
+     * @return CalendarEvent|null
+     */
+    protected static function normalizeVEventForDay(VEvent $vevent, string $slotKey, string $dateIso): ?CalendarEvent
+    {
+        if (!isset($vevent->DTSTART)) return null;
+
+        $isAllDay = strtoupper((string)($vevent->DTSTART['VALUE'] ?? '')) === 'DATE';
+        $start = self::toImmutable($vevent->DTSTART->getDateTime());
+        if ($start === null) return null;
+
+        $end = self::resolveEnd($vevent, $start, $isAllDay);
+
+        if (!self::intersectsDay($start, $end, $isAllDay, $dateIso)) return null;
+
+        $event = new CalendarEvent();
+        $event->slotKey = $slotKey;
+        $event->uid = trim((string)($vevent->UID ?? ''));
+        $event->recurrenceId = isset($vevent->{'RECURRENCE-ID'}) ? trim((string)$vevent->{'RECURRENCE-ID'}) : '';
+        $event->summary = trim((string)($vevent->SUMMARY ?? ''));
+        if ($event->summary === '') $event->summary = '(ohne Titel)';
+        $event->startIso = $start->format(DateTimeInterface::ATOM);
+        $event->endIso = $end->format(DateTimeInterface::ATOM);
+        $event->allDay = $isAllDay;
+        $event->time = $isAllDay ? '' : $start->format('H:i');
+        $event->location = trim((string)($vevent->LOCATION ?? ''));
+        $event->description = trim((string)($vevent->DESCRIPTION ?? ''));
+        $event->status = strtoupper(trim((string)($vevent->STATUS ?? '')));
+        $event->componentType = 'VEVENT';
+        $event->dateIso = $dateIso;
+
+        return $event;
+    }
+
+    /**
+     * Normalize a VEVENT into a CalendarEvent (without day filtering).
+     *
+     * @param VEvent $vevent
+     * @param string $slotKey
+     * @return CalendarEvent|null
+     */
+    protected static function normalizeVEvent(VEvent $vevent, string $slotKey): ?CalendarEvent
+    {
+        if (!isset($vevent->DTSTART)) return null;
+
+        $isAllDay = strtoupper((string)($vevent->DTSTART['VALUE'] ?? '')) === 'DATE';
+        $start = self::toImmutable($vevent->DTSTART->getDateTime());
+        if ($start === null) return null;
+
+        $end = self::resolveEnd($vevent, $start, $isAllDay);
+
+        $event = new CalendarEvent();
+        $event->slotKey = $slotKey;
+        $event->uid = trim((string)($vevent->UID ?? ''));
+        $event->recurrenceId = isset($vevent->{'RECURRENCE-ID'}) ? trim((string)$vevent->{'RECURRENCE-ID'}) : '';
+        $event->summary = trim((string)($vevent->SUMMARY ?? ''));
+        if ($event->summary === '') $event->summary = '(ohne Titel)';
+        $event->startIso = $start->format(DateTimeInterface::ATOM);
+        $event->endIso = $end->format(DateTimeInterface::ATOM);
+        $event->allDay = $isAllDay;
+        $event->time = $isAllDay ? '' : $start->format('H:i');
+        $event->location = trim((string)($vevent->LOCATION ?? ''));
+        $event->description = trim((string)($vevent->DESCRIPTION ?? ''));
+        $event->status = strtoupper(trim((string)($vevent->STATUS ?? '')));
+        $event->componentType = 'VEVENT';
+        $event->dateIso = $start->format('Y-m-d');
+
+        return $event;
+    }
+
+    /**
+     * Normalize a VTODO for a specific day.
+     *
+     * @param VTodo $vtodo
+     * @param string $slotKey
+     * @param string $dateIso
+     * @return CalendarEvent|null
+     */
+    protected static function normalizeVTodoForDay(VTodo $vtodo, string $slotKey, string $dateIso): ?CalendarEvent
+    {
+        $event = self::normalizeVTodo($vtodo, $slotKey);
+        if ($event === null) return null;
+
+        // Check if the VTODO's due/start date matches this day
+        if ($event->dateIso !== $dateIso) return null;
+
+        return $event;
+    }
+
+    /**
+     * Normalize a VTODO into a CalendarEvent.
+     *
+     * @param VTodo $vtodo
+     * @param string $slotKey
+     * @return CalendarEvent|null
+     */
+    protected static function normalizeVTodo(VTodo $vtodo, string $slotKey): ?CalendarEvent
+    {
+        // VTODO uses DUE or DTSTART for date
+        $dateProperty = $vtodo->DUE ?? $vtodo->DTSTART ?? null;
+        if ($dateProperty === null) return null;
+
+        $isAllDay = strtoupper((string)($dateProperty['VALUE'] ?? '')) === 'DATE';
+        $dt = self::toImmutable($dateProperty->getDateTime());
+        if ($dt === null) return null;
+
+        $event = new CalendarEvent();
+        $event->slotKey = $slotKey;
+        $event->uid = trim((string)($vtodo->UID ?? ''));
+        $event->recurrenceId = isset($vtodo->{'RECURRENCE-ID'}) ? trim((string)$vtodo->{'RECURRENCE-ID'}) : '';
+        $event->summary = trim((string)($vtodo->SUMMARY ?? ''));
+        if ($event->summary === '') $event->summary = '(ohne Titel)';
+        $event->startIso = $dt->format(DateTimeInterface::ATOM);
+        $event->endIso = '';
+        $event->allDay = $isAllDay;
+        $event->time = $isAllDay ? '' : $dt->format('H:i');
+        $event->location = trim((string)($vtodo->LOCATION ?? ''));
+        $event->description = trim((string)($vtodo->DESCRIPTION ?? ''));
+
+        $status = strtoupper(trim((string)($vtodo->STATUS ?? '')));
+        // Map VTODO statuses to our model
+        if ($status === 'COMPLETED') {
+            $event->status = 'COMPLETED';
+        } elseif ($status === 'IN-PROCESS' || $status === 'NEEDS-ACTION' || $status === '') {
+            $event->status = 'TODO';
+        } else {
+            $event->status = $status;
+        }
+
+        $event->componentType = 'VTODO';
+        $event->dateIso = $dt->format('Y-m-d');
+
+        return $event;
+    }
+
+    /**
+     * Resolve the end date/time for a VEVENT.
+     *
+     * @param VEvent $vevent
+     * @param DateTimeImmutable $start
+     * @param bool $isAllDay
+     * @return DateTimeImmutable
+     */
+    protected static function resolveEnd(VEvent $vevent, DateTimeImmutable $start, bool $isAllDay): DateTimeImmutable
+    {
+        if (isset($vevent->DTEND)) {
+            $end = self::toImmutable($vevent->DTEND->getDateTime());
+            if ($end !== null) return $end;
+        }
+
+        if (isset($vevent->DURATION)) {
+            try {
+                $duration = $vevent->DURATION->getDateInterval();
+                if ($duration instanceof DateInterval) {
+                    return $start->add($duration);
+                }
+            } catch (Throwable $e) {
+                // fall through
+            }
+        }
+
+        return $isAllDay ? $start->add(new DateInterval('P1D')) : $start;
+    }
+
+    /**
+     * Check if a date range intersects a given day.
+     *
+     * @param DateTimeImmutable $start
+     * @param DateTimeImmutable $end
+     * @param bool $isAllDay
+     * @param string $dateIso
+     * @return bool
+     */
+    protected static function intersectsDay(
+        DateTimeImmutable $start,
+        DateTimeImmutable $end,
+        bool $isAllDay,
+        string $dateIso
+    ): bool {
+        $eventTimezone = $start->getTimezone();
+        $dayStart = new DateTimeImmutable($dateIso . ' 00:00:00', $eventTimezone);
+        $dayEnd = $dayStart->add(new DateInterval('P1D'));
+
+        if ($end <= $start) {
+            $end = $isAllDay ? $start->add(new DateInterval('P1D')) : $start;
+        }
+
+        $intersects = ($start < $dayEnd) && ($end > $dayStart);
+        if (!$intersects && !$isAllDay && $start >= $dayStart && $start < $dayEnd && $end == $start) {
+            $intersects = true;
+        }
+
+        return $intersects;
+    }
+
+    /**
+     * Compare two CalendarEvents for sorting.
+     *
+     * @param CalendarEvent $a
+     * @param CalendarEvent $b
+     * @return int
+     */
+    protected static function compareEvents(CalendarEvent $a, CalendarEvent $b): int
+    {
+        if ($a->allDay !== $b->allDay) {
+            return $a->allDay ? -1 : 1;
+        }
+        $timeCmp = strcmp($a->time, $b->time);
+        if ($timeCmp !== 0) return $timeCmp;
+        return strcmp($a->summary, $b->summary);
+    }
+
+    /**
+     * Convert a DateTimeInterface to DateTimeImmutable.
+     *
+     * @param DateTimeInterface $dt
+     * @return DateTimeImmutable|null
+     */
+    protected static function toImmutable(DateTimeInterface $dt): ?DateTimeImmutable
+    {
+        if ($dt instanceof DateTimeImmutable) return $dt;
+        $immutable = DateTimeImmutable::createFromFormat('U', (string)$dt->getTimestamp());
+        if (!($immutable instanceof DateTimeImmutable)) return null;
+        return $immutable->setTimezone($dt->getTimezone());
+    }
+
+    /**
+     * Clear all runtime caches.
+     */
+    public static function clearCache(): void
+    {
+        self::$dayCache = [];
+        self::$taskCache = [];
+    }
+}
diff --git a/src/CalendarSlot.php b/src/CalendarSlot.php
new file mode 100644
index 0000000..10965a1
--- /dev/null
+++ b/src/CalendarSlot.php
@@ -0,0 +1,171 @@
+<?php
+
+namespace dokuwiki\plugin\luxtools;
+
+/**
+ * Represents one calendar slot configuration.
+ *
+ * Each slot has a stable key, a human-readable label, local/remote source
+ * configuration, a display color, and a derived enabled state.
+ */
+class CalendarSlot
+{
+    /** @var string[] Ordered list of all supported slot keys */
+    public const SLOT_KEYS = ['general', 'maintenance', 'slot3', 'slot4'];
+
+    /** @var array<string,string> Human-readable labels for slot keys */
+    public const SLOT_LABELS = [
+        'general'     => 'General',
+        'maintenance' => 'Maintenance',
+        'slot3'       => 'Slot 3',
+        'slot4'       => 'Slot 4',
+    ];
+
+    /** @var string */
+    protected $key;
+
+    /** @var string */
+    protected $label;
+
+    /** @var string Local ICS file path */
+    protected $file;
+
+    /** @var string CalDAV URL */
+    protected $caldavUrl;
+
+    /** @var string CalDAV username */
+    protected $username;
+
+    /** @var string CalDAV password */
+    protected $password;
+
+    /** @var string CSS color for widget indicators */
+    protected $color;
+
+    /**
+     * @param string $key
+     * @param string $file
+     * @param string $caldavUrl
+     * @param string $username
+     * @param string $password
+     * @param string $color
+     */
+    public function __construct(
+        string $key,
+        string $file = '',
+        string $caldavUrl = '',
+        string $username = '',
+        string $password = '',
+        string $color = ''
+    ) {
+        $this->key = $key;
+        $this->label = self::SLOT_LABELS[$key] ?? $key;
+        $this->file = trim($file);
+        $this->caldavUrl = trim($caldavUrl);
+        $this->username = trim($username);
+        $this->password = trim($password);
+        $this->color = trim($color);
+    }
+
+    public function getKey(): string
+    {
+        return $this->key;
+    }
+
+    public function getLabel(): string
+    {
+        return $this->label;
+    }
+
+    public function getFile(): string
+    {
+        return $this->file;
+    }
+
+    public function getCaldavUrl(): string
+    {
+        return $this->caldavUrl;
+    }
+
+    public function getUsername(): string
+    {
+        return $this->username;
+    }
+
+    public function getPassword(): string
+    {
+        return $this->password;
+    }
+
+    public function getColor(): string
+    {
+        return $this->color;
+    }
+
+    /**
+     * A slot is enabled if it has a local file path or a CalDAV URL.
+     *
+     * @return bool
+     */
+    public function isEnabled(): bool
+    {
+        return $this->file !== '' || $this->caldavUrl !== '';
+    }
+
+    /**
+     * Whether this slot has a usable local ICS file.
+     *
+     * @return bool
+     */
+    public function hasLocalFile(): bool
+    {
+        if ($this->file === '') return false;
+        return is_file($this->file) && is_readable($this->file);
+    }
+
+    /**
+     * Whether this slot has a configured remote CalDAV source.
+     *
+     * @return bool
+     */
+    public function hasRemoteSource(): bool
+    {
+        return $this->caldavUrl !== '';
+    }
+
+    /**
+     * Load all configured calendar slots from plugin configuration.
+     *
+     * @param object $plugin Plugin instance with getConf() method
+     * @return CalendarSlot[]  Keyed by slot key
+     */
+    public static function loadAll($plugin): array
+    {
+        $slots = [];
+        foreach (self::SLOT_KEYS as $key) {
+            $slots[$key] = new self(
+                $key,
+                (string)$plugin->getConf('calendar_' . $key . '_file'),
+                (string)$plugin->getConf('calendar_' . $key . '_caldav_url'),
+                (string)$plugin->getConf('calendar_' . $key . '_username'),
+                (string)$plugin->getConf('calendar_' . $key . '_password'),
+                (string)$plugin->getConf('calendar_' . $key . '_color')
+            );
+        }
+        return $slots;
+    }
+
+    /**
+     * Load only enabled calendar slots.
+     *
+     * @param object $plugin Plugin instance with getConf() method
+     * @return CalendarSlot[]  Keyed by slot key
+     */
+    public static function loadEnabled($plugin): array
+    {
+        $all = self::loadAll($plugin);
+        return array_filter($all, static function (CalendarSlot $slot): bool {
+            return $slot->isEnabled();
+        });
+    }
+}
diff --git a/src/ChronologicalCalendarWidget.php b/src/ChronologicalCalendarWidget.php
index 6236cda..66e3bc6 100644
--- a/src/ChronologicalCalendarWidget.php
+++ b/src/ChronologicalCalendarWidget.php
@@ -13,10 +13,17 @@ class ChronologicalCalendarWidget
      * @param int $year
      * @param int $month
      * @param string $baseNs
+     * @param array<string,string[]> $indicators  date => [slotKey, ...] from CalendarService::monthIndicators()
+     * @param array<string,string> $slotColors    slotKey => CSS color
      * @return string
      */
-    public static function render(int $year, int $month, string $baseNs = 'chronological'): string
-    {
+    public static function render(
+        int $year,
+        int $month,
+        string $baseNs = 'chronological',
+        array $indicators = [],
+        array $slotColors = []
+    ): string {
         if (!self::isValidMonth($year, $month)) return '';
 
         $firstDayTs = mktime(0, 0, 0, $month, 1, $year);
@@ -109,6 +116,19 @@ class ChronologicalCalendarWidget
                 $classes = 'luxtools-calendar-day';
 
                 $html .= '<td class="' . hsc($classes) . '" data-luxtools-date="' . hsc($date) . '">';
+
+                // Render slot indicators if any
+                $dayIndicators = $indicators[$date] ?? [];
+                if ($dayIndicators !== []) {
+                    $html .= '<div class="luxtools-calendar-indicators">';
+                    foreach ($dayIndicators as $slotKey) {
+                        $color = $slotColors[$slotKey] ?? '';
+                        $style = ($color !== '') ? ' style="background-color:' . hsc($color) . '"' : '';
+                        $html .= '<span class="luxtools-calendar-indicator luxtools-indicator-' . hsc($slotKey) . '"' . $style . '></span>';
+                    }
+                    $html .= '</div>';
+                }
+
                 if ($dayId !== null && function_exists('html_wikilink')) {
                     $html .= (string)html_wikilink($dayId, (string)$dayNumber);
                 } else {
diff --git a/src/IcsWriter.php b/src/IcsWriter.php
new file mode 100644
index 0000000..9b008d7
--- /dev/null
+++ b/src/IcsWriter.php
@@ -0,0 +1,434 @@
+<?php
+
+namespace dokuwiki\plugin\luxtools;
+
+use Sabre\VObject\Component\VCalendar;
+use Sabre\VObject\Component\VEvent;
+use Sabre\VObject\Component\VTodo;
+use Sabre\VObject\Reader;
+use Throwable;
+
+/**
+ * Write-back support for local ICS files.
+ *
+ * Handles updating event/task status (completion, reopening) in local
+ * ICS files while preserving the original component type and other properties.
+ */
+class IcsWriter
+{
+    /**
+     * Update the STATUS of an event or task occurrence in a local ICS file.
+     *
+     * For VEVENT: sets STATUS to the given value (TODO or COMPLETED).
+     * For VTODO: sets STATUS and, when completing, sets COMPLETED timestamp;
+     *            when reopening, removes the COMPLETED property.
+     *
+     * For recurring events, this writes an override/exception for the specific
+     * occurrence rather than modifying the master event.
+     *
+     * @param string $filePath  Absolute path to the local ICS file
+     * @param string $uid       Event UID
+     * @param string $recurrenceId  Recurrence ID (empty for non-recurring)
+     * @param string $newStatus     New status value (e.g. COMPLETED, TODO)
+     * @param string $dateIso       Occurrence date YYYY-MM-DD (for recurring event identification)
+     * @return bool  True if the file was updated successfully
+     */
+    public static function updateEventStatus(
+        string $filePath,
+        string $uid,
+        string $recurrenceId,
+        string $newStatus,
+        string $dateIso
+    ): bool {
+        if ($uid === '' || $filePath === '') return false;
+        if (!is_file($filePath) || !is_writable($filePath)) return false;
+
+        $raw = @file_get_contents($filePath);
+        if (!is_string($raw) || trim($raw) === '') return false;
+
+        try {
+            $calendar = Reader::read($raw, Reader::OPTION_FORGIVING);
+            if (!($calendar instanceof VCalendar)) return false;
+
+            $updated = self::applyStatusUpdate($calendar, $uid, $recurrenceId, $newStatus, $dateIso);
+            if (!$updated) return false;
+
+            $output = $calendar->serialize();
+            return self::atomicWrite($filePath, $output);
+        } catch (Throwable $e) {
+            return false;
+        }
+    }
+
+    /**
+     * Apply a status update to the matching component in the calendar.
+     *
+     * Public alias for use by CalDavClient when modifying remote calendar data.
+     *
+     * @param VCalendar $calendar
+     * @param string $uid
+     * @param string $recurrenceId
+     * @param string $newStatus
+     * @param string $dateIso
+     * @return bool  True if a component was updated
+     */
+    public static function applyStatusUpdateToCalendar(
+        VCalendar $calendar,
+        string $uid,
+        string $recurrenceId,
+        string $newStatus,
+        string $dateIso
+    ): bool {
+        return self::applyStatusUpdate($calendar, $uid, $recurrenceId, $newStatus, $dateIso);
+    }
+
+    /**
+     * Apply a status update to the matching component in the calendar.
+     *
+     * @param VCalendar $calendar
+     * @param string $uid
+     * @param string $recurrenceId
+     * @param string $newStatus
+     * @param string $dateIso
+     * @return bool  True if a component was updated
+     */
+    protected static function applyStatusUpdate(
+        VCalendar $calendar,
+        string $uid,
+        string $recurrenceId,
+        string $newStatus,
+        string $dateIso
+    ): bool {
+        // Try VEVENT first
+        foreach ($calendar->select('VEVENT') as $component) {
+            if (!($component instanceof VEvent)) continue;
+            if (self::matchesComponent($component, $uid, $recurrenceId, $dateIso)) {
+                self::setVEventStatus($component, $newStatus);
+                return true;
+            }
+        }
+
+        // Try VTODO
+        foreach ($calendar->select('VTODO') as $component) {
+            if (!($component instanceof VTodo)) continue;
+            if (self::matchesComponent($component, $uid, $recurrenceId, $dateIso)) {
+                self::setVTodoStatus($component, $newStatus);
+                return true;
+            }
+        }
+
+        // For recurring events without a matching override, create one
+        foreach ($calendar->select('VEVENT') as $component) {
+            if (!($component instanceof VEvent)) continue;
+            $componentUid = trim((string)($component->UID ?? ''));
+            if ($componentUid !== $uid) continue;
+
+            // This is the master event; check if it has RRULE (recurring)
+            if (!isset($component->RRULE)) continue;
+
+            // Create an occurrence override
+            $override = self::createOccurrenceOverride($calendar, $component, $newStatus, $dateIso);
+            if ($override !== null) return true;
+        }
+
+        // Same for VTODO with RRULE
+        foreach ($calendar->select('VTODO') as $component) {
+            if (!($component instanceof VTodo)) continue;
+            $componentUid = trim((string)($component->UID ?? ''));
+            if ($componentUid !== $uid) continue;
+
+            if (!isset($component->RRULE)) continue;
+
+            $override = self::createVTodoOccurrenceOverride($calendar, $component, $newStatus, $dateIso);
+            if ($override !== null) return true;
+        }
+
+        return false;
+    }
+
+    /**
+     * Check if a component matches the given UID and recurrence criteria.
+     *
+     * @param VEvent|VTodo $component
+     * @param string $uid
+     * @param string $recurrenceId
+     * @param string $dateIso
+     * @return bool
+     */
+    protected static function matchesComponent($component, string $uid, string $recurrenceId, string $dateIso): bool
+    {
+        $componentUid = trim((string)($component->UID ?? ''));
+        if ($componentUid !== $uid) return false;
+
+        // If we have a specific recurrence ID, match it
+        if ($recurrenceId !== '') {
+            $componentRid = isset($component->{'RECURRENCE-ID'}) ? trim((string)$component->{'RECURRENCE-ID'}) : '';
+            return $componentRid === $recurrenceId;
+        }
+
+        // For non-recurring events (no RRULE, no RECURRENCE-ID), match by UID alone
+        if (!isset($component->RRULE) && !isset($component->{'RECURRENCE-ID'})) {
+            return true;
+        }
+
+        // For a specific occurrence override already in the file
+        if (isset($component->{'RECURRENCE-ID'})) {
+            $ridDt = $component->{'RECURRENCE-ID'}->getDateTime();
+            if ($ridDt !== null && $ridDt->format('Y-m-d') === $dateIso) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    /**
+     * Set the STATUS property on a VEVENT.
+     *
+     * @param VEvent $vevent
+     * @param string $newStatus
+     */
+    protected static function setVEventStatus(VEvent $vevent, string $newStatus): void
+    {
+        $vevent->STATUS = $newStatus;
+    }
+
+    /**
+     * Set the STATUS property on a VTODO with native completion semantics.
+     *
+     * @param VTodo $vtodo
+     * @param string $newStatus
+     */
+    protected static function setVTodoStatus(VTodo $vtodo, string $newStatus): void
+    {
+        if ($newStatus === 'COMPLETED') {
+            $vtodo->STATUS = 'COMPLETED';
+            // Set COMPLETED timestamp per RFC 5545
+            $vtodo->COMPLETED = gmdate('Ymd\THis\Z');
+            // Set PERCENT-COMPLETE to 100
+            $vtodo->{'PERCENT-COMPLETE'} = '100';
+        } else {
+            // Reopening
+            $vtodo->STATUS = 'NEEDS-ACTION';
+            // Remove COMPLETED timestamp
+            if (isset($vtodo->COMPLETED)) {
+                unset($vtodo->COMPLETED);
+            }
+            if (isset($vtodo->{'PERCENT-COMPLETE'})) {
+                unset($vtodo->{'PERCENT-COMPLETE'});
+            }
+        }
+    }
+
+    /**
+     * Create an occurrence override for a recurring VEVENT.
+     *
+     * @param VCalendar $calendar
+     * @param VEvent $master
+     * @param string $newStatus
+     * @param string $dateIso
+     * @return VEvent|null
+     */
+    protected static function createOccurrenceOverride(
+        VCalendar $calendar,
+        VEvent $master,
+        string $newStatus,
+        string $dateIso
+    ): ?VEvent {
+        try {
+            $isAllDay = strtoupper((string)($master->DTSTART['VALUE'] ?? '')) === 'DATE';
+
+            $props = [
+                'UID' => (string)$master->UID,
+                'SUMMARY' => (string)($master->SUMMARY ?? ''),
+                'STATUS' => $newStatus,
+            ];
+
+            if ($isAllDay) {
+                $recurrenceValue = str_replace('-', '', $dateIso);
+                $props['DTSTART'] = $recurrenceValue;
+                $props['RECURRENCE-ID'] = $recurrenceValue;
+                // Set VALUE=DATE on the properties
+                $override = $calendar->add('VEVENT', $props);
+                $override->DTSTART['VALUE'] = 'DATE';
+                $override->{'RECURRENCE-ID'}['VALUE'] = 'DATE';
+            } else {
+                // Use the master's time for the occurrence
+                $masterStart = $master->DTSTART->getDateTime();
+                $recurrenceValue = $dateIso . 'T' . $masterStart->format('His');
+                $tz = $masterStart->getTimezone();
+                if ($tz && $tz->getName() !== 'UTC') {
+                    $props['DTSTART'] = $recurrenceValue;
+                    $props['RECURRENCE-ID'] = $recurrenceValue;
+                    $override = $calendar->add('VEVENT', $props);
+                    $override->DTSTART['TZID'] = $tz->getName();
+                    $override->{'RECURRENCE-ID'}['TZID'] = $tz->getName();
+                } else {
+                    $recurrenceValue .= 'Z';
+                    $props['DTSTART'] = $recurrenceValue;
+                    $props['RECURRENCE-ID'] = $recurrenceValue;
+                    $override = $calendar->add('VEVENT', $props);
+                }
+            }
+
+            // Copy duration or DTEND if present
+            if (isset($master->DTEND)) {
+                $duration = $master->DTSTART->getDateTime()->diff($master->DTEND->getDateTime());
+                $startDt = $override->DTSTART->getDateTime();
+                $endDt = $startDt->add($duration);
+                if ($isAllDay) {
+                    $override->add('DTEND', $endDt->format('Ymd'));
+                    $override->DTEND['VALUE'] = 'DATE';
+                } else {
+                    $override->add('DTEND', $endDt);
+                }
+            } elseif (isset($master->DURATION)) {
+                $override->DURATION = (string)$master->DURATION;
+            }
+
+            // Copy LOCATION and DESCRIPTION if present
+            if (isset($master->LOCATION)) {
+                $override->LOCATION = (string)$master->LOCATION;
+            }
+            if (isset($master->DESCRIPTION)) {
+                $override->DESCRIPTION = (string)$master->DESCRIPTION;
+            }
+
+            return $override;
+        } catch (Throwable $e) {
+            return null;
+        }
+    }
+
+    /**
+     * Create an occurrence override for a recurring VTODO.
+     *
+     * @param VCalendar $calendar
+     * @param VTodo $master
+     * @param string $newStatus
+     * @param string $dateIso
+     * @return VTodo|null
+     */
+    protected static function createVTodoOccurrenceOverride(
+        VCalendar $calendar,
+        VTodo $master,
+        string $newStatus,
+        string $dateIso
+    ): ?VTodo {
+        try {
+            $dateProperty = $master->DUE ?? $master->DTSTART ?? null;
+            $isAllDay = $dateProperty !== null && strtoupper((string)($dateProperty['VALUE'] ?? '')) === 'DATE';
+
+            $props = [
+                'UID' => (string)$master->UID,
+                'SUMMARY' => (string)($master->SUMMARY ?? ''),
+            ];
+
+            if ($isAllDay) {
+                $recurrenceValue = str_replace('-', '', $dateIso);
+                if (isset($master->DTSTART)) {
+                    $props['DTSTART'] = $recurrenceValue;
+                }
+                if (isset($master->DUE)) {
+                    $props['DUE'] = $recurrenceValue;
+                }
+                $props['RECURRENCE-ID'] = $recurrenceValue;
+
+                $override = $calendar->add('VTODO', $props);
+
+                if (isset($override->DTSTART)) {
+                    $override->DTSTART['VALUE'] = 'DATE';
+                }
+                if (isset($override->DUE)) {
+                    $override->DUE['VALUE'] = 'DATE';
+                }
+                $override->{'RECURRENCE-ID'}['VALUE'] = 'DATE';
+            } else {
+                $dt = $dateProperty->getDateTime();
+                $recurrenceValue = $dateIso . 'T' . $dt->format('His');
+                $tz = $dt->getTimezone();
+                if ($tz && $tz->getName() !== 'UTC') {
+                    if (isset($master->DTSTART)) {
+                        $props['DTSTART'] = $recurrenceValue;
+                    }
+                    if (isset($master->DUE)) {
+                        $props['DUE'] = $recurrenceValue;
+                    }
+                    $props['RECURRENCE-ID'] = $recurrenceValue;
+                    $override = $calendar->add('VTODO', $props);
+                    if (isset($override->DTSTART)) {
+                        $override->DTSTART['TZID'] = $tz->getName();
+                    }
+                    if (isset($override->DUE)) {
+                        $override->DUE['TZID'] = $tz->getName();
+                    }
+                    $override->{'RECURRENCE-ID'}['TZID'] = $tz->getName();
+                } else {
+                    $recurrenceValue .= 'Z';
+                    if (isset($master->DTSTART)) {
+                        $props['DTSTART'] = $recurrenceValue;
+                    }
+                    if (isset($master->DUE)) {
+                        $props['DUE'] = $recurrenceValue;
+                    }
+                    $props['RECURRENCE-ID'] = $recurrenceValue;
+                    $override = $calendar->add('VTODO', $props);
+                }
+            }
+
+            self::setVTodoStatus($override, $newStatus);
+
+            if (isset($master->LOCATION)) {
+                $override->LOCATION = (string)$master->LOCATION;
+            }
+            if (isset($master->DESCRIPTION)) {
+                $override->DESCRIPTION = (string)$master->DESCRIPTION;
+            }
+
+            return $override;
+        } catch (Throwable $e) {
+            return null;
+        }
+    }
+
+    /**
+     * Public atomic file write for use by CalDavClient sync.
+     *
+     * @param string $filePath
+     * @param string $content
+     * @return bool
+     */
+    public static function atomicWritePublic(string $filePath, string $content): bool
+    {
+        $dir = dirname($filePath);
+        if (!is_dir($dir)) {
+            @mkdir($dir, 0755, true);
+        }
+        return self::atomicWrite($filePath, $content);
+    }
+
+    /**
+     * Atomic file write using a temp file and rename.
+     *
+     * @param string $filePath
+     * @param string $content
+     * @return bool
+     */
+    protected static function atomicWrite(string $filePath, string $content): bool
+    {
+        $dir = dirname($filePath);
+        $tmpFile = $dir . '/.luxtools_tmp_' . getmypid() . '_' . mt_rand();
+
+        if (@file_put_contents($tmpFile, $content, LOCK_EX) === false) {
+            @unlink($tmpFile);
+            return false;
+        }
+
+        if (!@rename($tmpFile, $filePath)) {
+            @unlink($tmpFile);
+            return false;
+        }
+
+        return true;
+    }
+}
diff --git a/style.css b/style.css
index 8e15cc4..6270400 100644
--- a/style.css
+++ b/style.css
@@ -646,3 +646,241 @@ div.luxtools-calendar td.luxtools-calendar-day:hover {
 div.luxtools-calendar td.luxtools-calendar-day.luxtools-calendar-day-today:hover {
     background-color: @ini_highlight;
 }
+
+/* ============================================================
+ * Calendar Widget Indicators
+ * Colored corner markers showing which slots have events on a day.
+ * Positions: general=top-left, maintenance=top-right,
+ *            slot3=bottom-right, slot4=bottom-left (clockwise)
+ * ============================================================ */
+div.luxtools-calendar td.luxtools-calendar-day {
+    position: relative;
+}
+
+.luxtools-calendar-indicators {
+    position: absolute;
+    top: 0;
+    left: 0;
+    right: 0;
+    bottom: 0;
+    pointer-events: none;
+}
+
+.luxtools-calendar-indicator {
+    position: absolute;
+    width: 6px;
+    height: 6px;
+    border-radius: 50%;
+}
+
+.luxtools-indicator-general {
+    top: 2px;
+    left: 2px;
+}
+
+.luxtools-indicator-maintenance {
+    top: 2px;
+    right: 2px;
+}
+
+.luxtools-indicator-slot3 {
+    bottom: 2px;
+    right: 2px;
+}
+
+.luxtools-indicator-slot4 {
+    bottom: 2px;
+    left: 2px;
+}
+
+
+/* ============================================================
+ * Chronological Events on Day Pages
+ * ============================================================ */
+div.luxtools-chronological-events ul {
+    list-style: none;
+    padding-left: 0;
+    margin: 0.5em 0;
+}
+
+div.luxtools-chronological-events li {
+    padding: 0.35em 0.5em;
+    margin: 0.25em 0;
+    border-left: 3px solid @ini_border;
+    cursor: pointer;
+}
+
+div.luxtools-chronological-events li:hover {
+    background-color: @ini_background_alt;
+}
+
+div.luxtools-chronological-events li[data-luxtools-event] .luxtools-event-time {
+    font-weight: bold;
+    margin-right: 0.25em;
+}
+
+
+/* ============================================================
+ * Maintenance Tasks
+ * ============================================================ */
+div.luxtools-chronological-maintenance li {
+    border-left-color: #e67e22;
+}
+
+li.luxtools-maintenance-task.luxtools-task-completed {
+    opacity: 0.5;
+    text-decoration: line-through;
+}
+
+button.luxtools-task-action,
+button.luxtools-task-complete-btn {
+    margin-left: 0.5em;
+    padding: 0.15em 0.5em;
+    font-size: 0.85em;
+    border: 1px solid @ini_border;
+    border-radius: 0.2em;
+    background-color: @ini_background_alt;
+    cursor: pointer;
+}
+
+button.luxtools-task-action:hover,
+button.luxtools-task-complete-btn:hover {
+    background-color: @ini_highlight;
+}
+
+button.luxtools-task-action:disabled,
+button.luxtools-task-complete-btn:disabled {
+    opacity: 0.5;
+    cursor: wait;
+}
+
+
+/* ============================================================
+ * Maintenance Task List (syntax plugin)
+ * ============================================================ */
+div.luxtools-maintenance-tasks {
+    margin: 1em 0;
+}
+
+ul.luxtools-maintenance-task-list {
+    list-style: none;
+    padding-left: 0;
+}
+
+ul.luxtools-maintenance-task-list li {
+    padding: 0.35em 0.5em;
+    margin: 0.25em 0;
+    border-left: 3px solid #e67e22;
+}
+
+li.luxtools-task-overdue .luxtools-task-date {
+    color: #c0392b;
+    font-weight: bold;
+}
+
+.luxtools-task-date {
+    font-family: monospace;
+    margin-right: 0.5em;
+}
+
+.luxtools-task-time {
+    font-weight: bold;
+    margin-right: 0.25em;
+}
+
+.luxtools-maintenance-task-item.luxtools-task-completed {
+    opacity: 0.5;
+    text-decoration: line-through;
+}
+
+
+/* ============================================================
+ * Event Popup
+ * ============================================================ */
+.luxtools-event-popup-overlay {
+    display: none;
+    position: fixed;
+    top: 0;
+    left: 0;
+    width: 100%;
+    height: 100%;
+    background: rgba(0, 0, 0, 0.4);
+    z-index: 10000;
+    justify-content: center;
+    align-items: center;
+}
+
+.luxtools-event-popup {
+    background: @ini_background;
+    border: 1px solid @ini_border;
+    border-radius: 0.4em;
+    padding: 1.5em;
+    max-width: 500px;
+    width: 90%;
+    max-height: 80vh;
+    overflow-y: auto;
+    position: relative;
+    box-shadow: 0 4px 20px rgba(0, 0, 0, 0.3);
+}
+
+.luxtools-event-popup-close {
+    position: absolute;
+    top: 0.5em;
+    right: 0.75em;
+    background: none;
+    border: none;
+    font-size: 1.5em;
+    cursor: pointer;
+    color: @ini_text;
+    line-height: 1;
+}
+
+.luxtools-event-popup-close:hover {
+    opacity: 0.7;
+}
+
+.luxtools-event-popup-title {
+    margin: 0 0 0.75em 0;
+    padding-right: 1.5em;
+}
+
+.luxtools-event-popup-field {
+    margin: 0.5em 0;
+}
+
+.luxtools-event-popup-description {
+    white-space: pre-wrap;
+    word-break: break-word;
+}
+
+.luxtools-event-popup-slot {
+    margin-top: 1em;
+    opacity: 0.6;
+    font-size: 0.9em;
+}
+
+
+/* ============================================================
+ * Notifications (fallback)
+ * ============================================================ */
+.luxtools-notification {
+    position: fixed;
+    top: 1em;
+    right: 1em;
+    z-index: 10001;
+    padding: 0.75em 1em;
+    border-radius: 0.3em;
+    font-size: 0.9em;
+    max-width: 400px;
+    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.3);
+}
+
+.luxtools-notification-error {
+    background: #c0392b;
+    color: #fff;
+}
+
+.luxtools-notification-warning {
+    background: #e67e22;
+    color: #fff;
+}
diff --git a/syntax/calendar.php b/syntax/calendar.php
index 6ba22a3..a06f822 100644
--- a/syntax/calendar.php
+++ b/syntax/calendar.php
@@ -1,6 +1,8 @@
 <?php
 
 use dokuwiki\Extension\SyntaxPlugin;
+use dokuwiki\plugin\luxtools\CalendarService;
+use dokuwiki\plugin\luxtools\CalendarSlot;
 use dokuwiki\plugin\luxtools\ChronologicalCalendarWidget;
 
 require_once(__DIR__ . '/../autoload.php');
@@ -85,7 +87,18 @@ class syntax_plugin_luxtools_calendar extends SyntaxPlugin
         $month = (int)$data['month'];
         $baseNs = (string)$data['base'];
 
-        $renderer->doc .= ChronologicalCalendarWidget::render($year, $month, $baseNs);
+        // Load slot indicators and colors for the calendar widget
+        $slots = CalendarSlot::loadEnabled($this);
+        $indicators = CalendarService::monthIndicators($slots, $year, $month);
+        $slotColors = [];
+        foreach ($slots as $slot) {
+            $color = $slot->getColor();
+            if ($color !== '') {
+                $slotColors[$slot->getKey()] = $color;
+            }
+        }
+
+        $renderer->doc .= ChronologicalCalendarWidget::render($year, $month, $baseNs, $indicators, $slotColors);
 
         return true;
     }
diff --git a/syntax/maintenance.php b/syntax/maintenance.php
new file mode 100644
index 0000000..e7614ee
--- /dev/null
+++ b/syntax/maintenance.php
@@ -0,0 +1,129 @@
+<?php
+
+use dokuwiki\Extension\SyntaxPlugin;
+use dokuwiki\plugin\luxtools\CalendarService;
+use dokuwiki\plugin\luxtools\CalendarSlot;
+use dokuwiki\plugin\luxtools\ChronoID;
+
+require_once(__DIR__ . '/../autoload.php');
+
+/**
+ * luxtools Plugin: Maintenance task list syntax.
+ *
+ * Renders a list of all non-completed maintenance tasks due today or earlier.
+ *
+ * Syntax:
+ *   {{maintenance_tasks>}}
+ */
+class syntax_plugin_luxtools_maintenance extends SyntaxPlugin
+{
+    /** @inheritdoc */
+    public function getType()
+    {
+        return 'substition';
+    }
+
+    /** @inheritdoc */
+    public function getPType()
+    {
+        return 'block';
+    }
+
+    /** @inheritdoc */
+    public function getSort()
+    {
+        return 225;
+    }
+
+    /** @inheritdoc */
+    public function connectTo($mode)
+    {
+        $this->Lexer->addSpecialPattern(
+            '\{\{maintenance_tasks>\}\}',
+            $mode,
+            'plugin_luxtools_maintenance'
+        );
+    }
+
+    /** @inheritdoc */
+    public function handle($match, $state, $pos, Doku_Handler $handler)
+    {
+        return ['ok' => true];
+    }
+
+    /** @inheritdoc */
+    public function render($format, Doku_Renderer $renderer, $data)
+    {
+        if ($data === false || !is_array($data)) return false;
+        if ($format !== 'xhtml') return false;
+        if (!($renderer instanceof Doku_Renderer_xhtml)) return false;
+
+        $renderer->nocache();
+
+        $slots = CalendarSlot::loadAll($this);
+        $maintenanceSlot = $slots['maintenance'] ?? null;
+
+        if ($maintenanceSlot === null || !$maintenanceSlot->isEnabled()) {
+            $renderer->doc .= '<div class="luxtools-plugin luxtools-maintenance-tasks">'
+                . '<p class="luxtools-empty">'
+                . hsc($this->getLang('maintenance_no_tasks'))
+                . '</p></div>';
+            return true;
+        }
+
+        $todayIso = date('Y-m-d');
+        $tasks = CalendarService::openMaintenanceTasks($maintenanceSlot, $todayIso);
+
+        $title = (string)$this->getLang('chronological_maintenance_title');
+        if ($title === '') $title = 'Tasks';
+
+        $renderer->doc .= '<div class="luxtools-plugin luxtools-maintenance-tasks">';
+        $renderer->doc .= '<h3>' . hsc($title) . '</h3>';
+
+        if ($tasks === []) {
+            $noTasks = (string)$this->getLang('maintenance_no_tasks');
+            if ($noTasks === '') $noTasks = 'No open tasks.';
+            $renderer->doc .= '<p class="luxtools-empty">' . hsc($noTasks) . '</p>';
+        } else {
+            $renderer->doc .= '<ul class="luxtools-maintenance-task-list">';
+            foreach ($tasks as $task) {
+                $overdue = ($task->dateIso < $todayIso);
+                $classes = 'luxtools-maintenance-task-item';
+                if ($overdue) {
+                    $classes .= ' luxtools-task-overdue';
+                }
+
+                $renderer->doc .= '<li class="' . $classes . '"';
+                $renderer->doc .= ' data-uid="' . hsc($task->uid) . '"';
+                $renderer->doc .= ' data-date="' . hsc($task->dateIso) . '"';
+                $renderer->doc .= ' data-recurrence="' . hsc($task->recurrenceId) . '"';
+                $renderer->doc .= '>';
+
+                // Date badge
+                $renderer->doc .= '<span class="luxtools-task-date">' . hsc($task->dateIso) . '</span> ';
+
+                // Time if not all-day
+                if ($task->time !== '') {
+                    $renderer->doc .= '<span class="luxtools-task-time">' . hsc($task->time) . '</span> ';
+                }
+
+                // Summary
+                $renderer->doc .= '<span class="luxtools-task-summary">' . hsc($task->summary) . '</span>';
+
+                // Complete button
+                $completeLabel = (string)$this->getLang('maintenance_task_complete');
+                if ($completeLabel === '') $completeLabel = 'Complete';
+                $renderer->doc .= ' <button class="luxtools-task-complete-btn" type="button"'
+                    . ' data-action="complete"'
+                    . '>' . hsc($completeLabel) . '</button>';
+
+                $renderer->doc .= '</li>';
+            }
+            $renderer->doc .= '</ul>';
+        }
+
+        $renderer->doc .= '</div>';
+
+        return true;
+    }
+}