CalDav Server:

• Baïkal CalDav Server (PHP, SQLite)

Clients:

• PC: Vivaldi (and KOrganizer for importing ICS files and syncing them to CalDav Server)
• Android: DAVx⁵ for Syncing Calendars to device, ICSx⁵ for syncing external WebICS Calendars.
• org.fossify.calendar as GUI to the calendars.

Open Problems:

• Sharing Calendars, see https://www.ncartron.org/sharing-calendars-with-baikal.html and https://devblog.yvn.no/posts/baikal-caldav-hosting/