Citadel began in December 1981 as a dialup BBS package written by Jeff Prothero (CrT) for 8-bit CP/M systems. It collected some remarkably favorable reactions, being praised for its streamlined and easy to learn user interface. During these early years, the single-user Citadel code was ported to many of the popular microcomputer platforms of the era, such as Tony Preston's Citadel-68K Amiga port, and Vince Quaresima's Citadel-K2NE MS-DOS port. Hue White's Citadel-86 port was also popular in some parts of the world.
Art Cancro brought up the first multiuser implementation of Citadel in March 1988, running on an Altos unix system. This site is still running today, with a long and storied history of its own. Citadel-UX, as this implementation was initially known, shared the same user interface as its peers, and had much of the same on-disk architecture, but enjoyed a ground-up rewrite of the internals to support multiple concurrent users. One site had six phone lines, in fact, demonstrating that unix systems could easily accomplish concurrency that required multiple computers to accomplish with MS-DOS.
In the 1990s, Citadel became quite popular as a platform for the online communities of that time. Nearly every popular site was a fork of Citadel, such as "DaveCode" and "DOC" which ran absolutely massive communities. This was an exciting era of the Internet when many new users were signing on, but before mainstream social media sites monopolized the public mindshare, so online communities were very popular.
Beginning in the mid 1990s, Citadel began to undergo the transformation into the modern collaborative software we know today. The "groupware" effort began with developers and system administrators frustrated with the poor quality of commercial solutions such as Exchange and Notes, and with the byzantine complexity of the primitive open source solutions available at the time. Citadel already had the framework in place to be a flexible, powerful communications server. The program was split into client and server portions, a web based user interface was created, and the server architecture was made more robust, supporting heavier loads and all of the common Internet-facing protocols.
As the user community grew for Linux and open source in general, and Citadel in particular, a great deal of effort has focused on making the Citadel system as easy to install as possible. Part of this effort has involved keeping the number of external dependencies to a minimum. While many of the competing solutions (many of them now obsolete) were basically just roll-ups of existing packages lashed together with a management framework, Citadel's developers took the time to carefully implement each service, carefully and tightly integrated into the rest of the system. This accounts for Citadel's scalability and minimal resource requirements. New users find the Citadel system easy to install, even if they are relatively new to the administration of Linux and open source.
Collaboration is at the heart of life on the Internet, and Citadel is uniquely positioned to be a part of it. We look forward to implementing every popular "decentralized" and/or "federated" standard that comes into existence, and we look forward to being a core component of the free world, outside the confines of the eavesdropped, censored, and suppressive worlds of the Silicon Valley giants. Join us!