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Horde Groupware vs Citadel: catalog facts
Horde Groupware	Citadel
Free Free and open source with no paid tier.	Free Free and open source under the GNU GPL, with no paid edition.
Web, Self-hosted	Web, Self-hosted
Full groupware suite beyond mail, including tasks, notes and time tracking CalDAV, CardDAV and ActiveSync sync	Mail, calendar, contacts, forums, wiki and chat in one server Consistent rooms-based structure across features
Requires running and maintaining a PHP server Older codebase with a long history of security fixes to track	The rooms metaphor differs from conventional mail servers Requires running and maintaining your own server
Self-hosted	Self-hosted
Open source	Open source
License: LGPL/GPL	License: GPL
Not stated if an account is 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 September 23, 2026	Official website Full listing and sources Checked October 2, 2026

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