Dawn of the Ages  
   A player kill MUD. Written in Java for a new, stable codebase.
   http://dawn.netcologne.de

Materia Magica  
   Features forums, online status indicators, and references.
   http://www.materiamagica.com

LegendMUD  
   Features a variety of historical contexts, including ancient Ireland, Homer, Queen Elizabeth, Dante's Inferno, goldrush Melbourne, and Kipling's India. Supports a variety of styles of play.
   http://www.legendmud.org/

Angalon  
   A medieval theme. Features sections on theme, players, beginner's guide, message board and immortals.
   http://angalon.tamu.edu

Symelion  
   Science fiction roleplaying via web-based chatrooms.
   http://www.geocities.com/Area51/Comet/1416

Abydos  
   Made from scratch in Delphi, screenshots are available on the homepage. Medieval based, newbie friendly.
   http://www.abydos.nl/

The World of Shadowgate  
   Written using Standard MUDLIB much like C++.
   http://www.firedragon.com

UrMud  
   Set in ancient history featuring a self-growing ecology, advanced combat system, houses and clans.
   http://urmud.com/

Ursha Null 7  
   A science fiction mud. Features sections on game play and technical information.
   http://www.ursha7.com

Banished Lands  
   Sections on online help, players, areas, rules and policy, clans and brethren.
   http://banished.dentinmud.org

The Land of Drogon  
   A multi-user reality in the style of a traditional adventure like Zork or Colossal Cave.
   http://www.drogon.net/tlod/

MUDII  
   MUD2 is the latest incarnation of the very first MUD (Essex MUD/MUD1/British Legends.)
   http://www.mudii.co.uk/

Forest Edge Building Manual  
   Information on building rooms, mobiles, objects, shops and pets.
   http://www.geocities.com/tri_deryck/manual.html

British Legends  
   A port of the Compuserve incarnation of the original Multi-User Dungeon, written by Richard Bartle and Roy Trubshaw. Offers detailed assistance to new players, FAQs and a brief history.
   http://www.british-legends.com/

Monster  
   A multiplayer adventure game for VMS.
   http://www.skrenta.com/monster/

DestinyForge  
   Gaming Engine running Realtime and Turn based Fantasy Wargames.
   http://www.DestinyForge.co.uk/

Alternate Universe MUD  
   Alternate Universe is a free online multiplayer game, inspired by science-fiction, and entirely custom-written in Java. Includes codewars extension.
   http://www.btinternet.com/~duncan.jauncey/mud/

SocketMud  
   Bareboned MUD codebase written in C, and is available for download.
   http://www.daimi.au.dk/~jobo/socketmud/