Radicale is a small but powerful CalDAV (calendars, to-do lists) and CardDAV (contacts) server
* Shares calendars and contact lists through CalDAV, CardDAV and HTTP.
* Supports events, todos, journal entries and business cards.
* Works out-of-the-box, no complicated setup or configuration required.
* Can limit access by authentication.
* Can secure connections with TLS.
* Works with many CalDAV and CardDAV clients.
* Stores all data on the file system in a simple folder structure.
* Can be extended with plugins.
* Is GPLv3-licensed free software.