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Nextcloud Calendar vs Citadel: catalog facts
Nextcloud Calendar	Citadel
Free Free app for Nextcloud servers.	Free Free and open source under the GNU GPL, with no paid edition.
Web, Self-hosted	Web, Self-hosted
Calendars stay on your own server CalDAV sync with standard clients	Mail, calendar, contacts, forums, wiki and chat in one server Consistent rooms-based structure across features
Requires a running Nextcloud server Not a standalone app	The rooms metaphor differs from conventional mail servers Requires running and maintaining your own server
Self-hosted	Self-hosted
Open source	Open source
License not stated	License: GPL
Account needed	Not stated if an account is needed
Not stated if it works offline	Not stated if it works offline
Official website Full listing and sources Checked October 2, 2026	Official website Full listing and sources Checked October 2, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.