MUDs

DizzyMud
Entertainment, Games, Online, MUDs, Diku - Dizzymud. Provides various roleplaying formats and is based on a combination of fantasy and science fiction themes.
https://dizzymud.com/
DIKU MUD - DIKU MUD
Entertainment, Games, Online, MUDs, Diku - Diku MUD. Official Diku website, featuring a heirarchy, and copyright issues with Everquest.
https://www.dikumud.com/
The Northern Crossroads
Northern Crossroads MUD is a free text-based adventure game that has been in operation since 1992.
http://www.ncmud.org
Legends of Kallisti
Entertainment, Games, Online, MUDs, Diku - Kallisti MUD. Features include in-depth guides about classes, races, spells, skills, and equipment, overviews of many game features, builder information, MSP sound information, and message forums.
http://www.kallistimud.com
The Underworld MUD
A stable mud with 65 mortal levels, lots of spells and skills, as well as friendly players and Gods!
https://www.theuw.net/
Zee MUD
Entertainment, Games, Online, MUDs, Diku - Zee Mud. Swords and sorcery theme Dikumud based upon Mudde Pathetique.
http://www.zeemud.org
Medievia - Do You Dare Enter?
Entertainment, Games, Online, MUDs, Diku - Medievia. One of the largest, most advanced games on the Internet.
http://www.medievia.com