Open-source calendars

7 calendars whose code is public under an OSI-approved license, rated for privacy with evidence. Picks first, then by score.

1. Baïkal Grade B

   Self-hosted CalDAV and CardDAV server written in PHP and built on the sabre/dav library, with a web interface for managing users, calendars and address books.

   GPL-3.0. Source code

2. DAVx⁵ Grade B

   Android app that syncs calendars, contacts, tasks and files with CalDAV, CardDAV and WebDAV servers, so they appear in the device's own calendar and contacts apps.

   GPL-3.0. Source code

3. Etar Grade B

   Open source Android calendar app based on the AOSP Calendar. Shows calendars stored on the device, including offline calendars and CalDAV calendars synced by an app such as DAVx5.

   GPL-3.0. Source code

4. Fossify Calendar Grade B

   Offline Android calendar from Fossify, a community fork of Simple Mobile Tools. Supports widgets, reminders and ICS import and export, and can show CalDAV calendars synced by an app such as DAVx5.

   GPL-3.0. Source code

5. KashCal Grade B

   Offline-first Android calendar that syncs with iCloud, CalDAV and the device calendar. Needs no account, has no telemetry and stores credentials in the Android Keystore.

   Apache-2.0. Source code

6. Nextcloud Calendar Grade B

   Calendar app for self-hosted Nextcloud servers. Syncs across devices with CalDAV and supports shared calendars and appointment booking. No end-to-end encryption.

   AGPL-3.0. Source code

7. Radicale Grade B

   Lightweight self-hosted CalDAV and CardDAV server written in Python, for syncing calendars, contacts and task lists across devices. Stores data as plain files.

   GPL-3.0. Source code

Compare all 12 calendars, open source or not.