Radicale VS EteSync Server

Maybe https://radicale.org/ could fit the bill, CalDav for as a calendar server and CardDav for contacts.

I now use CalDAV Synchronizer to sync Outlook to my Radicale CalDAV / CardDAV "server" (a Raspberry Pi), with DAVx running on our phones.

Also look at Baikal, in addtion to Radicale.

Setup: 1. Install a CalDev server on my home server (running Debian Linux) using maybe Radicale (https://radicale.org/) 2. Use the Linux version of ProtonMail Bridge on this server to set up IMAP to connect to this CalDev server 3. Configure filters to automatically forward event invites sent to my ProtonMail address to my CalDev server, decrypted by Bridge 4. Configure my CalDev server to use ProtonMail to send event invites, when I create new events and add invitees 5. Add this CalDev server to Fantastical, using the app on iOS and MacOS as my primary calendar

Caldav is what you are looking for. The other comments mention implementations of them and i can vouch for radicale pretty barebones but does its job

We are thinking of writing a guide to setting up a small Radicale instance. This could be hosted on a raspberry pi, or small NAS or something.

After trying a number of alternatives, I'm strongly recommending radicale.

I used this as a guide, but made some changes to it: https://github.com/Kozea/Radicale/issues/779

Are you / have you considered leveraging postgres' row level security for this (row filtering)? Feels like a natural fit for ensuring the right subset of data gets to the right users https://www.postgresql.org/docs/current/ddl-rowsecurity.html

E2E encryption would also be nice to have, it could be worth having a look at https://www.etesync.com/ for inspiration

A few days ago I saw some guys in this community saying that they uses https://www.etesync.com/ in order to sync contacts between Proton + Thunderbird (Desktop) + Mobile. I haven't used it yet, but I saved the link.

https://inteltechniques.com/book7a.html Benefits of iOS Risks of iOS Privacy & Security Considerations Settings Remove unused stock apps App Store login vs iCloud login App funding DNS: https://nextdns.io/ Calendars & Contacts: https://www.etesync.com/ Password Manager: https://strongboxsafe.com/ VoIP App: https://acrobits.net/ VoIP Service: https://voip.ms/en/invite/Mzc2NjM3 Data Service: https://refer.telnyx.com/refer/zrfmo Custom App Settings Shortcuts for Home Screen Next Week

EteSync - Secure Data Sync (version 2.4.0): Secure, private and end-to-end encrypted calendar, contacts and tasks sync

The programs will allow me to sync both my Google and my Etesyc Contacts and Calendars. Etesync also needs Etesync-Dav installed on the desktop but that is well explained on Github.

There is https://www.etesync.com