Citadel/UX (typically referred to simply as "Citadel") is a collaboration suite (messaging and groupware) that is descended from the

Citadel A citadel is the core fortified area of a town or city. It may be a castle, fortress, or fortified center. The term is a diminutive of "city", meaning "little city", because it is a smaller part of the city of which it is the defensive core. In ...

family of programs which became popular in the 1980s and 1990s as a

bulletin board system A bulletin board system (BBS), also called computer bulletin board service (CBBS), is a computer server running software that allows users to connect to the system using a terminal program. Once logged in, the user can perform functions such ...

platform. It is designed to run on open source operating systems such as

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, whi ...

or BSD. Although it is being used for many bulletin board systems, in 1998 the developers began to expand its functionality to a general purpose groupware platform. In order to modernize the Citadel platform for the

Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, p ...

, the Citadel/UX developers added functionality such as shared calendars, instant messaging, and built-in implementations of Internet protocols such as

SMTP The Simple Mail Transfer Protocol (SMTP) is an Internet standard communication protocol for electronic mail transmission. Mail servers and other message transfer agents use SMTP to send and receive mail messages. User-level email clients ty ...

IMAP In computing, the Internet Message Access Protocol (IMAP) is an Internet standard protocol used by email clients to retrieve email messages from a mail server over a TCP/IP connection. IMAP is defined by . IMAP was designed with the goal of per ...

Sieve A sieve, fine mesh strainer, or sift, is a device for separating wanted elements from unwanted material or for controlling the particle size distribution of a sample, using a screen such as a woven mesh or net or perforated sheet materia ...

POP3 In computing, the Post Office Protocol (POP) is an application-layer Internet standard protocol used by e-mail clients to retrieve e-mail from a mail server. POP version 3 (POP3) is the version in common use, and along with IMAP the most common ...

, GroupDAV and

XMPP Extensible Messaging and Presence Protocol (XMPP, originally named Jabber) is an open communication protocol designed for instant messaging (IM), presence information, and contact list maintenance. Based on XML (Extensible Markup Language), i ...

. All protocols offer

OpenSSL OpenSSL is a software library for applications that provide secure communications over computer networks against eavesdropping or need to identify the party at the other end. It is widely used by Internet servers, including the majority of HT ...

encryption for additional security. Users of Citadel/UX systems also have available to them a web-based user interface which employs

Ajax Ajax may refer to: Greek mythology and tragedy * Ajax the Great, a Greek mythological hero, son of King Telamon and Periboea * Ajax the Lesser, a Greek mythological hero, son of Oileus, the king of Locris * ''Ajax'' (play), by the ancient Gree ...

style functionality to allow application-like interaction with the system. Citadel uses the

Berkeley DB Berkeley DB (BDB) is an unmaintained embedded database software library for key/value data, historically significant in open source software. Berkeley DB is written in C with API bindings for many other programming languages. BDB stores arbitr ...

database for all of its data stores, including the message base. Citadel/UX became

free and open-source software Free and open-source software (FOSS) is a term used to refer to groups of software consisting of both free software and open-source software where anyone is freely licensed to use, copy, study, and change the software in any way, and the source ...

subject to the terms of the GPL-2.0-or-later license in 1998. In 2006 Citadel was relicensed to the GPL-2.0-only license. In 2007 Citadel was relicensed again to the GPL-3.0-only license.

References

External links

* * Review of Citadel by Carla Schroder of Enterprise Networking Planet
Part 1Part 2

Mod_auth_citadel
an Apache Web Server authentication module for Citadel by Stuart Cianos {{DEFAULTSORT:Citadel Ux Free groupware Bulletin board system software Collaborative software for Linux Ajax (programming) Free email server software Free email software Free content management systems Formerly proprietary software