MusicMUD is third-generation MUD engine. It is written predominantly in C++, with substantial amounts of Lua, both as a scripting language and as a secondary implementation language.
We started this engine in the late 90s, learning lessons from previous MUD codebases we were familiar with. We define a data-driven world model, stored in a data dictionary, with capacity for arbitrary customisation with C++ modules, lua verbs & an extensive system of events.
We last did a tested mainline public release in 2003, but you can look at our source tree on github, which is periodically updated from the Cryosphere private repo. The codebase is still undergoing modernisation.
It's licenced under the GNU General Public Licence, version 2, or at your option any later version. Note: we do not consider a game world written for musicmud, or code written in lua to interface with it, a derivative work of musicmud.