Baïkal

Baïkal is a lightweight CalDAV and CardDAV server that lets you host your own calendars and contacts. DAV-compatible clients sync against your server rather than a hosted account, keeping the data on infrastructure you control.

Calendars use CalDAV and contacts use CardDAV. A web interface handles management of users, address books, and calendars, and data is stored in a MySQL or SQLite database. It runs on a basic PHP server and works with iOS, macOS, DAVx5 on Android, Mozilla Thunderbird, and other CalDAV and CardDAV clients.

Baïkal is built on the sabre/dav library and is released under the GNU GPL v3. It was created by Jérôme Schneider of Net Gusto and fruux and is now developed by volunteers.