DemiMUD is a MUD codebase written in Rust.
Main repo is at: https://github.com/andreivasiliu/demimud
This little CLI is DemiMUD compiled as a simple stdin-reading single-player binary... so it's more of a SUD. Also, combat is not implemented, so it's more just a thing than a dungeon. So, welcome to DemiSUT, I suppose!
3.5MB out of the 4MB are area text files, imported from the Dawn of Time v1.69r MUD by Michael Garratt (c) 1997-2004. DemiMUD(/SUT?) has less than 1% of DoT's features, but it's made to be able to import its areas and let you walk around the world. The MudSchool area's triggers are also somewhat functional.