Check out . Linder is a programming language designed specifically for the creation of muds. It is fast, easy to learn and very powerful with ActiveX support, Running as a 2000/XP/NT service, object orientated or functional design, powerful command parser and lots of other mud-related features.

It looks quite interesting, although the platform is a bit of a limitation, and it's still very early in development. Personally I'd be more tempted to go for something like LPC or ColdC, both of which are also languages designed specifically for creating muds.