A great company that has IMO created the two best MUDs ever.

Their first of their games that was a great success was Gemstone III, which is by far my favorite MUD. It is so completely different from the standard MUD created by someone who changes a few lines of code and claims to have created an original game. It has a great atmosphere because roleplaying is encouraged and acting blatantly OOC isn't allowed.

Dragonrealms is Simutronics' other popular MUD. It is like Gemstone III in some ways, but it seems like a more serious game for experienced MUD players. It uses an original skill system where you get better at things by doing them, instead of the standard training points system.

Simutronics has a large staff for each game, working both in-game helping people resolve problems and hosting special events (such as tournaments, merchants, and auctions), and designing new spells, skills, items, areas, and other additions to the games. Each game has no problem supporting the approximately 1000 connections that they generally have during the day.

The price of $10/month to play one of their MUDs is definitely worth it, as no free MUD I've seen has even come close to being as good as them.