MUD stands for Multi-User Dungeon. I’ve heard of people say that the D stands for Dimension instead of Dungeon, but I’m going with Dungeon, in spite of the fact that my first MUD isn’t a dungeon.
One of the great things about making a text-based MUD is that it lets me do all kinds of things with world-building that would be pretty much impossible if I had to have 3d (or even 2d) graphics for everything. I’m fascinated with the idea of generating stories and emergent stories, and MUDs are a perfect platform for working with stories in that way.
I’m using Evennia to make my MUD. It uses Python, which is my favorite programming language. It’s powerful, well-designed, well-documented, and has a good community.