I'm not so sure about MUD 'creators', but there's a lot of MUD codebases for you to work with. Take a Google around for "MUD codebases".
My personal recommendation (ie. the MUD codebase I first started with way back when) is with CircleMUD, however. I found it simpler to use than a lot of the bulkier ones, and pretty easy to get running.
However, the majority of MUD codebases are written in C, so either be sure to have some prior programming knowledge, or move into this with a lot of patience, and be prepared for lots of hard work irregardless of your choice. Creating anysort of online game is a difficult and rewarding experience.
Good luck!
