AberMUD
No sub-categories 2 Sites Avalon
No sub-categories 2 Sites DikuMUD
CircleMUD, Merc, Silly, TFE, VME 85 Sites Independent Development
Materia Magica 16 Sites LambdaMOO
No sub-categories 2 Sites LP
Ancient Anguish, Discworld, Fantasy, Genesis, LPC, ... 49 Sites MajorMud
Chats and Forums 14 Sites

Mordor
Hrielith, Isengard 4 Sites MUCKs
Anime, Fantasy, FAQs, Help, and Tutorials, Furry, ... 31 Sites MUD2
No sub-categories 4 Sites MUSH
Anime, Comics, Fantasy, Resources, Science Fiction, ... 33 Sites Rapture
No sub-categories 5 Sites TinyMUD
No sub-categories 1 Sites

Codebases
Online : MUDs : Development 66 Sites