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Citadel vs Horde Groupware: catalog facts
Citadel	Horde Groupware
Free Free and open source under the GNU GPL, with no paid edition.	Free Free and open source with no paid tier.
Web, Self-hosted	Web, Self-hosted
Mail, calendar, contacts, forums, wiki and chat in one server Consistent rooms-based structure across features	Full groupware suite beyond mail, including tasks, notes and time tracking CalDAV, CardDAV and ActiveSync sync
The rooms metaphor differs from conventional mail servers Requires running and maintaining your own server	Requires running and maintaining a PHP server Older codebase with a long history of security fixes to track
Self-hosted	Self-hosted
Open source	Open source
License: GPL	License: LGPL/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 October 2, 2026	Official website Full listing and sources Checked September 23, 2026

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