I fear you may be in danger after viewing this screenshot.
That’s Threshold, a role playing multi-user dungeon with a history that goes all the way back to the Pentium generation. Don’t get too close, or it’ll suck you in. 😯
Threshold isn’t the software running though; that’s tintin, the client.
I have little experience with MUDs, unless you can count Crawl as one, and I don’t think it does.
tintin should work with games beyond Threshold though. So if you get bored with that one, there should be others available to you.