The MUDDL programming language, "Multi User Dungeon Definition Language", is a domain-specific language for creation of text-based multi-user virtual worlds, i.e. MUDs. The first version of it was written by Richard Bartle and Roy Trubshaw in BCPL; it was later ported to C++ by Viktor Toth. It was originally used to implement MUD1, and was later used for a number of other MUDs, such as MIST.
↑Bartle, Richard (2002). "Incarnations of MUD". "Viktor Toth had had a copy of the BCPL source code for MUD1 for some years, and decided that now was the time to do something with it. In a 9-day programming blitz over Christmas, he rewrote the BCPL MUDDL engine in C++ and opened it up alongside MUD2. The ex-CompuServe players gravitated there, where it now runs as a direct continuation of the defunct original BL incarnation."
↑Bartle, Richard (1999). "MUDDL". "Many MUDDL databases were written by students at Essex University, the most well-known being 'Mist', 'Rock', 'Blud' and 'Uni' [...]"