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Citadel vs grommunio: catalog facts
Citadel	grommunio
Free Free and open source under the GNU GPL, with no paid edition.	Freemium Open source, with paid plans listed on the pricing page.
Web, Self-hosted	Linux, Web, Self-hosted
Mail, calendar, contacts, forums, wiki and chat in one server Consistent rooms-based structure across features	Native MAPI, EWS and EAS support for Outlook and mobile clients Mail, calendars, chat, video and files on one platform
The rooms metaphor differs from conventional mail servers Requires running and maintaining your own server	Running a groupware server requires administration skills Some features may depend on paid plans
Self-hosted	Self-hosted, Hosted service
Open source	Open source
License: GPL	License not stated
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 October 1, 2026

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