Citadel – groupware software

Citadel/UX (commonly known as Citadel) is an open source, complete and feature-rich collaboration suite (messaging and groupware). Citadel delivers an Exchange-killer groupware server, a web and telnettable BBS, and an online PIM suite using the standard GroupDAV protocol. Citadel has been widely popular as a bulletin board system platform.

In order to modernize the Citadel platform, the developers have added additional functionality such as shared calendars, instant messaging, and built-in implementations of Internet protocols such as SMTP, IMAP, Sieve, POP3, and GroupDAV. All protocols offer OpenSSL encryption for additional security.

The key to Citadel’s versatility is its unique architecture. A Citadel system is made up of containers called “rooms”. A room may be used as an email folder, a discussion forum, a real-time chat, a mailing list, a calendar, an address book, an RSS reader, or several of these at the same time. Users can also distribute a Citadel installation across multiple servers, allowing unlimited horizontal scalability.

The Citadel system is extremely versatile. It provides numerous front ends to present to users, such as a text-based interface, an AJAX-style web interface known as Webcit, and many popular PIM clients using SMTP/POP/IMAP

Unlike many other groupware servers, Citadel is not a cut-down version of an expensive proprietary ‘professional’ version. It also provides its own data stores and is therefore extremely easy to install.

Features include:

  • Easy to administer.
  • Email, calendaring/scheduling, address books, bulletin boards, instant messaging, multiple domain support all coupled with a modern AJAX-style web interface.
  • High-performance, multiprotocol, multithreaded server engine.
  • Access to web browser, telnet/SSH and local client software.
  • Integrated server-side mail sorting and filtering. Users can choose between an easy-to-use web based rules editor, or the power of writing complex scripts using the industry standard Sieve language.
  • Group calendaring and scheduling: compatible with GroupDAV and Kolab.
  • Equipped with built-in email filtering technologies such as SpamAssassin, Realtime Blackhole Lists (RBL’s) and ClamAV antivirus.
  • Authenticated SMTP for remote email submission.
  • Support for push e-mail and mobile devices.
  • Enables server-to-server replication. that implies user user in any number of domain can spread to any number of Citadel servers.
  • Provides strong support for public folders and message forums.
  • Built-in listserv (mailing list server).
  • Server-to-server replication. Users in any number of domains can be spread out across any number of Citadel servers, allowing users to put data where they need it, and enabling infinite horizontal scalability.
  • Web-based access to email, calendars, and everything else through a powerful AJAX-style front end.
  • Good documentation.

Support: Documentation
License: GNU GPL v3


Citadel is written in C. Learn C with our recommended free books and free tutorials.

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