Calypso is a CalDAV/CardDAV server on Linux.

Calypso works with evolution, iceowl and the Android CalDAV/CardDAV
plugins. It does not yet work with aCal; for some reason aCal cannot
find any calendars on the server.

Calypso also supports importing calendar changes from the command
line, allowing you to integrate support into a text-based email
application like notmuch or mutt.