Etesync

[seeker]

Secure, end-to-end encrypted, and privacy respecting sync for your contacts, calendars, tasks and notes.

Easy to use and open source - it seamlessly integrates with your existing apps so you won't even notice you are using it!

https://www.etesync.com/

https://github.com/etesync/server

Interview

[necrevistonnezr]

Already here: https://forum.cloudron.io/post/3924

[girish]

Locking as dup