LambdaMOO

LambdaMOO's virtual world is centered on a digital recreation of Pavel Curtis's California home. A coat closet serves as the spawn point leading to the living room, an important social organ of the house. The house contains functioning appliances and can be explored in its entirety, even including the ductwork, hidden rooms and an underground complex.

The neighborhood immediately surrounding the house can also be explored, though the hazardous edge of the world is a short distance away. In addition, certain ornaments throughout the house can be entered to visit entirely different areas, such as an Alpine village in a snow globe or a hotel game piece on a Monopoly board. The world is user-generated.

LambdaMOO has its roots in the 1978–1980 work by Roy Trubshaw and Richard Bartle to create and expand the concept of Multi-User Dungeon (MUD) – virtual communities. Around 1987–1988, the expansion of the global Internet allowed more users to experience the MUD. Pavel Curtis at Xerox PARC noted that they were "almost exclusively for recreational purposes." Curtis determined to explore whether the MUD could be non-recreational.

He developed LambdaMOO software to run on the LambdaMOO server, which implements the MOO programming language. This software was subsequently made available to the public. Several starter databases, known as cores, are available for MOOs; LambdaMOO itself uses the LambdaCore database. The "Lambda" name is from Curtis's own username on earlier MUD systems.