The LPmud driver is quite some insane piece of work, considering it was done in 1990/91 initially. It is a VM, OOP C dialect featuring lists and hashtables (LPC), has lambda-closures (and things like map() + filter() with that), and allowed reloading of most parts of the game without having to restart the entire MUD for that, a big issue Diku and others suffered from. There were a number of spawn-offs from that like MudOS and there was something called LPC4 which eventually morphed into Pike, the language the Roxen webserver was/is written in. I actually used that on my local machine over Apache, because configuring latter back in the early days was a nightmare while Roxen had a pretty simple and straightforward webinterface for that already.

LPmud eventually got developed further and runs under the LDmud label now.

The MUDs based on LPmud/LDmud are quite diverse and are interesting in themselves, if you have access to their core sources. I also remember statically linking MudOS which resulted in a binary of like 500kB back in time, meaning it was possible to use that as a very powerful scripting language in embedded systems.