Instead of Google Calendar

Shared calendars, invites and reminders.

Swap it

CalDAV is an old, boring standard and it works. Nextcloud is the easy path; Radicale is the small one.

You lose: Invites across companies, which mostly still work, and the mobile apps people already know.

Start here

Nextcloud Calendar

AGPL-3.0an eveningactive

CalDAV plus a decent web UI. Mobile apps are third-party and fine.

github.com/nextcloud/server nextcloud.com

A compose file, a domain and a reverse proxy.

Also worth a look

RadicaleGPL-3.0a containeractive
A CalDAV server and nothing else. No web interface worth using.
github.com/Kozea/Radicale radicale.org
BaikalGPL-3.0a containeractive
CalDAV and CardDAV with a small admin UI. Feature-frozen but stable.
github.com/sabre-io/Baikal sabre.io/baikal

Facts checked 8 November 2026. Licences, activity and archive status come from each project's own repository; the verdict and the cost lines are the desk's.