https://f-droid.org/packages/com.etesync.syncadapter/
EteSync - Secure Data Sync | F-Droid - Free and Open Source Android App Repository
Secure, private and end-to-end encrypted calendar, contacts and tasks sync
sync f droidetesync secure
https://www.etesync.com/
EteSync - Secure Data Sync
Secure, end-to-end encrypted, and privacy respecting sync for your contacts, calendars, tasks and notes.
etesync securedata
https://pim.etesync.com/signup
EteSync - Secure Data Sync
etesync securedata