I loved MUDs as a kid, and really do miss the sense of immersion and depth that came from joining a long established server and just exploring.
I had a blast in the late 2000s joining dead MUDs and just wandering around. It was utterly bizarre, in a good way. It also felt somewhat shocking when someone else actually signed in.
It is very strange to me when people refer generically to "MUD" and cannot even seem to qualify what type of MUD they refer to.
Since the advent of MUD gaming, there has been a wide variety of codebases, servers, and clients, with distinct genealogical lineages, that appeal to quite distinct sectors of nerd-dom, and sometimes with very little overlap in the player base.
The original big-3 "non-Tiny" MUDs were: AberMUD, DikuMUD, and LPMud. These were largely unknown to me as I never played any of them, but they were mostly known as combat-based, player-programmable, and even quite distinctly European, for the most part. I could be wrong.
TinyMUD Classic began at CMU with Jim Aspnes, but quicky a lot of forks developed that resulted in MUCK, MUSH, MOO, FuzzBall and other interesting derivatives. The Tiny* class shared a lot of playerbase, because the appeal was mostly the same; all were user-extensible but only some were programmable; none were combat-based or adversarial. They mostly tended to evolve into social and chat functions, once they were established and built-up.
There are plenty of other MUD types and in the 90s, every budding programmer had ideas and forked a codebase for their own purposes. But it still baffles me, when commenters here and there wax nostalgic about those MUD days, I really have no idea what sort of game they're referring to, if they cannot be more specific.
I have a love/hate relationship with my memories of the MUD era. I loved exploring different worlds and interacting with some of the brilliant people who took the time to help teach and encourage others. I was a casual who would disappear for months at a time when doing real world things, but it was comforting to be able to come back a little community of people building fun things.
The couple MUD communities I participated in eventually collapsed under drama explosions from terminally online people. Some really manipulative and cruel stuff from people who would present themselves as noble community leaders, work themselves into positions of power, then grind down everyone in the out group until the rest of the community stopped playing.
I would log in to a couple of them once a year. It was the same small ingroup of people idling away. All the recent posts on the in-game message board were from the new people complaining, admonishing, or introducing more rules to tighten their grip on anyone who remained. Really sad to see the same pattern collapse multiple different communities in the same way.