I'm tied to a piece of software called WorldGroup, which is a stupidly expensive hosting environment for several types of online systems, but the one in particular that I'm involved in is an older gaming environment which I've been running for several years that still has a notable following called MajorMud. I've also written a few support modules for it that I sell on the side.
There's always been talk of porting it, but it just never happens. If it ever does happen, I'll most likely dump Windows in favor of just about anything else that supports WorldGroup. I'm not holding my breath though, fortunately. :-)