Groupware and bulletin board for Linux
Citadel consists of an SMTP, a POP3 and an IMAP server capable of filtering emails via Sieve. The software offers discussion forums, calendars, address books, task managers, instant messaging, and a web mailer (Webcit). Many of these features are accessible via GroupDAV. The Citadel software is based on a bulletin board system developed back in 1987. It can be found in many Linux distributions, although not always in its latest version. The Citadel web site describes the easy install auto-build process.