Hi!
EteSync is a CalDAV server and app, that let the user sync contacts, calendars and tasks between multiple devices with end-to-end encryption, so that the sync server cannot access this data.
Android App is free and open-source. EteSync provides a paid managed instance, but the server and the web app are open-source and can be self-hosted.
It would be great if linuxserver.io team could create a Docker image for that.