start - Citadel.org

Powerful and flexible

Citadel is easy, versatile, and powerful, thanks to its exclusive "rooms" based architecture. No other platform seamlessly combines so many different features using this familiar and consistent metaphor.

Packed with features

email
calendar/scheduling
address books
bulletin boards (forums)
mailing list server
instant messaging
wiki and blog engines
multiple domain support
a powerful web interface
see the full feature list...

True open source

Citadel is 100% open source software using the GNU General Public License. It's not a crippled, cut-down version of some expensive "enterprise" edition. The software you download here is the very best available, and it's all free software.