Shadowrun Denver is currently the most active Shadowrun MUSH around. The game operates on 3rd edition rules, with no immediate plans to change to 4th. Logins typically average 30-40 people during peak hours, which are evenings EST.

For the unfamiliar, Shadowrun is a table-top game (like D&D) set in the near future. Cyberpunk elements play a heavy role in the atmosphere. As is typical for that sort of theme, the old governments have collapsed, replaced by powerful megacorporations. Cyborgs roam the streets, and gangers control the slums where much of the unfortunate populace lives. With Shadowrun, however, there are many differences.

Shadowrun introduces fantasy elements into the cyberpunk genre. There's magic, variants of humanity (dwarves, elves, orks, trolls), and even supernatural creatures. Several corporations are controlled by dragons! The average person is aware of the fact that magic exists, but is otherwise usually unfamiliar with its workings.

Denver has been around for many years now. Today, it's the only active MUSH offering the Shadowrun experience. As someone who has played on both the player and staff side of things, I know that Denver is not without its problems. That said, it remains a great place to enjoy the setting. Rarely is there a time where roleplay isn't available. Something's always going on, and players have the freedom to run their own Shadowruns (mercenary jobs, like D&D adventures) if they wish.

The MUSH is quite open in terms of what you're allowed to play. All of the basic archetypes (samurai, adept, mage, shaman, decker, rigger, face) are allowed. Some people portray traditionally non-PC archetypes as well, such as enchanters, fixers, and gangers. Many elements from Magic in the Shadows/Cannon Companion/Matrix and others are utilized, though some are not. It's best to check in-game for that.

If you enjoy a gritty setting with some unusual thematic elements, I'd encourage you to check out Denver. People are very friendly on the Newbie channel and will gladly answer questions. My character, Gruk, could use some people in his gang! Instant RP hook for you.