I'm working on a mud (multiplayer text game) engine and I would like developers to be able to write their game logic in any programming language. Does anyone know if other engines like this exist?
MUDs typically have a text interface accessible via a simple TCP stream.
Developers who wish to write game logic in arbitrary languages could simply have their programs interface with the MUD back-end via that text interface. Let them log into pseudo-characters and send text commands to the back-end, and receive results across that existing interface.
This approach would work for any language which supports opening a TCP network connection, and the engine then doesn't have to care at all about what language individual developers use, since it's interacting with them across a generic text interface.
There is - and can't be - a system which accepts any language. After all, to achieve that goal, somebody would have to add compilers or interpreters for languages like Piet or Befunge. While this is certainly possible for any given language, it's not possible for all of them - while you're implementing them, somebody will just invent a bunch of new ones.
That said, there are common virtual machines which already have compilers for a lot of languages each. All you have to do is to build the engine around those VMs. The three most commonly encountered are:
Short answer: No there is no mud-engine that accepts any language.
There is probably nothing at all that accepts 'ALL' languages (except for the keyboard and still I'm not sure).
That said, I'd suggest that you make the core (the engine) in whatever language you want and then offer bindings to the most common languages used, for example:
Those are either scripting languages with big communities around them or languages that are used by a lot of programmers.
I'd just go for Lua though (or another well known scripting language) for starters and add other ones as per request when the API and the engine is ready.