Looking for a calendaring companion to Sylpheed on Trisquel Mini

The MATE Indicator Applet has the Ayatana Application Indicator that provides short access to app menus like Redshift, Transmission, Gajim and several others. The Ayatana Datetime Indicator seems to show events from the evolution server only, if it is installed. So this would be about a calendaring app that could either send menu items and relevant data to the Application indicator (I believe this is called SNI for Status Notifier Item) or just send its events to the Datetime indicator like evolution does.

LXDE is using its in-house indicator applets, although it looks like the Ayatana Indicators could also be used. The general idea would be to get the coming calendar events to show on the small calendar that can be accessed by clicking on the default clock. This is the closest I could find for now: https://lxde-list.narkive.com/ZjWM6AyS/lxpanel-patch-make-the-calendar-show-details. Sadly, all that remains of that great project is an archived 2013 thread.

It appears that the best candidate for the time being is Osmo. The project has been revived and is currently actively maintained. It does looks like a good PIM companion to Sylpheed/Claws: not as minimalist as when, but still reasonably lightweight. It only pulled two small dependencies and it just works. For now at least.

It does send neat event notifications (sound and pop-up), and on LXDE the icon shows as expected in the notification area. This provides a clean way to minimize the application window while still getting notified of coming events, and a basic menu with shortcuts to the main views. So there is still room for improvement but it seems to be going in the right direction.