Sync your contacts, calendars and tasks.

Radicale is a small but powerful CalDAV (calendars, to-do lists) and CardDAV (contacts) server, that:

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.