Citadel

Citadel is an open source software for email, collaboration, groupware and content management that is quick to set-up on a company's hardware or in the cloud. It is 100% free open source, and its codebase is written mostly in C while 100% of its code is covered by the GNU General Public License.

Citadel is a highly integrated groupware platform with AJAX-powered "Web 2.0" interface, but also providing built-in email SMTP, IMAP, POP3, Group calendaring and scheduling (WebDAV, GroupDAV, and Kolab-1 compatible), address books, and bulletin boards.

Citadel has a built-in: Wiki and blog engines, listserv (mailing list server), full-text index for fast searching, instant messaging, RSS Feed Aggregation, and integration with perimeter email filtering technologies.

Citadel provides a high-performance, multiprotocol, multithreaded server engine, an integrated server-side mail sorting and filtering, and server-to-server replication so that users in many domains can be spread out across any number of Citadel servers. Citadel is accessible through a web-browser for access to emails, calendars and more, and also through telnet/SSH, and local client software.

Citadel is database-driven, single-instance message store with multiple domain support as well as support for "public folders" and message forums. Citadel delivers authenticated SMTP for remote email submission, and it offers SSL/TLS encryption for all protocols.

Citadel is easy, versatile, and powerful, thanks to its exclusive "rooms" based architecture, it offers a one-step installer that automatically downloads, installs, and configures the complete Citadel system on a computer. It is easy to install nature eliminates source code manually, and it eliminates package dependency problems.