Radicale is a small but powerful CalDAV (calendars, todo-lists) and CardDAV (contacts) server

* Shares calendars through CalDAV, WebDAV and HTTP.
* Shares contacts through CardDAV, WebDAV and HTTP.
* Supports events, todos, journal entries and business cards.
* Works out-of-the-box, no installation nor configuration required.
* Can warn users on concurrent editing.
* Can limit access by authentication.
* Can secure connections.
* Works with many CalDAV and CardDAV clients.
* Is GPLv3-licensed free software.