I have a MUD that I don't think has ever been listed here before. I discovered it about a week ago. It's a MUSH, its based off of Star Trek TOS, after the Undiscovered Country movie. It is RPI, and if Star Trek isn't your thing, this place won't be for you. This game has apparently been picked up when its predecessor went down some time ago.
It doesn't have a lot of players, but those players that are there now have been through all of the previous game's history and have been involved in this genre for a long time. I've found everyone there to be friendly and helpful.
So what does this game have? It has a very vast and complex space system where each officer or crew member has a vital role to play. It has planets and outpost and bases and other places to travel. There is a fully simulated aspect of needing to do your part, such as in engineering, you would man the console there and provide power to each system, adjusting the balance depending on what is needed from the bridge. It has working hand weaponry such as phasers, as well as equipment like tricorders, medkits, engineering tool kits, and communicators. The ship also has comm panels so that each station can contact another area of the ship, i.e. bridge asking for more power to the engines from Engineering.
SO, now that I've given an idea of what it has for features, let me go over what it is not. It is not a Miriani, Prometheus, SC, CR, or any such clone. It is not a solo experience, roleplay is required, hence the RPI noted above. It is not a type of MUD where you type a few commands and you're in a new place in seconds. Traveling takes time, sometimes hours. The roleplay is turn based, that is, if you're used to RPing on CR, or those other types of MUDs, this isn't the style done here. It's turn based, as in, someone starts with their pose, and it rotates through everyone who is there, and then back to the start. You don't jump in the middle and start acting out things. It is also a slower-paced style of RP. For instance, it might take anywhere from a minute to five minutes to see another's pose. IT has powerful RP tools such as @emit, which basically lets you emote or pose without your name appearing in the text. This is good, because it allows you to be a lot more flexible with your RP, but it could also be used for bad purposes, which should be avoided, etc. Despite it being RPI, it does actually have a few OOC channels, they're listed out and you can join or create your own, the one you'll be auto-joined to when you create is PUB. Since the player base is currently small, most of the players are on one ship known as the USS Excalibur. This is to keep everyone together so that there are folks to RP with.
The connection info is: TOS.TREKMUSH.NET port 1701. I hope I've written this in such a way that you don't have to try it if you don't think it will be what you want. I realize this type of thing is a niche, but if you think it might be something you're interested in, give it a try. It is one of those MUDs where the people are often idle, and when they come active is usually in the evenings my time, which is EST or GMT - 05:00. The admin behind it seemed a bit skeptical about screen readers and such when I first joined, but he was able to get their web client working with screen readers. I've tested it with Chrome and Safari on iOS, and it does work. I've never seen that type of thing before, usually those clients are completely unusable by us. He has also created a screen reader flag, and says he will keep that thing in mind when working on new systems, to cut out things like ascii borders and the like. Anyway, like I said, give it a shot if you think you might be interested, if not, no harm in just passing it by, but I do quite enjoy it.