The first open-source MUD, written by the famous Alan Cox of Linux fame.
The codebase was updated over time, but its truest contribution was the revolution it began. It served as the inspiration to the three great open-source codebases that they and their progeny would dominate in the Internet for the next 30 years.
He actually was working on AberMUD, and his own Operating System, when he first heard about Linux (Linux Journal Staff, 2000).
Alan Cox was quite familiar with MUDs, having actually played on the original MUD, going by the name 'Anarchy'. (Antell, 1991)
The MUD is so-named because Alan was working on it while at the Aberystwyth University.
AberMUD II was the last original final version. It was picked back up in 1989 with the AberMUD 1989 version. That was eventually followed by versions 4 and 5 by other coders. Usually any pre-compiled versions of AberMUD will be from version II and most tools were made with AberMUD II specifically in mind. So anything 3rd party programs or assets may be incompatible with anything past the 1989 update.
On December 3rd, 1996, AberMUD and its original database were placed under the GPL by Alan Cox and Dick Porter.
Linux Journal Staff (June 13, 2000) An interview with alan cox. Linux Journal. Retrieved from https://www.linuxjournal.com/article/5045 Last retrieved on December 1st, 2018.
Antell, K.M. (April 19, 1991) MUD info. MUD History. Retrieved from https://www.landley.net/history/mirror/games/mud-history.html
B, then C
Anyone going west from here will explode