EnvyMUD is a MUD

MUD

A MUD , pronounced , is a multiplayer real-time virtual world, with the term usually referring to text-based instances of these. MUDs combine elements of role-playing games, hack and slash, player versus player, interactive fiction, and online chat...

 codebase written by Michael Chastain, Michael Quan, Mitchell Tse, David Love, and Guilherme Arnold which was created in 1994 as a derivate of the Merc

Merc (MUD)

Merc is a MUD engine derived from Copper, which in turn was based on DikuMUD. First released in March 1991, DikuMUD served as the basis for many later MUDs....

 codebase which itself was based on DikuMUD

DikuMUD

DikuMUD is a multiplayer text-based role-playing game, which is a type of MUD. It was written in 1990 and 1991 by Sebastian Hammer, Tom Madsen, Katja Nyboe, Michael Seifert, and Hans Henrik Staerfeldt at DIKU —the department of computer science at the University of Copenhagen in Copenhagen,...

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EnvyMUD had two major release versions: the original release (1.0) in 1994, and version 2.0 in 1995. The latest release version is 2.2 that was finalized in 1997.