LogiMOO: An extensible multi-user virtual world with natural language control. LogiMOO is a BinProlog-based virtual world running under netscape and internet explorer for distributed group-work over the internet and user-crafted virtual places, virtual objects and agents. LogiMOO is implemented on top of a multi-threaded blackboard-based logic programming system (BinProlog) featuring Linda-style coordination. Remote and local blackboards support transparent distribution of data and processing over TCP/IP links, while threads ensure high-performance local client-server dynamics. Embedding in netscape provides advanced VRML and HTML frame-based navigation and multi-media support, while LogiMOO handles virtual presence and acts as a very high-level multi-media object broker. User-friendliness is achieved through a controlled English interface written in terms of assumption grammars. Its language coverage is extensible in that the user can incorporate new nouns, verbs and adjectives as needed by changes in the world. Immediate evaluation of world knowledge by the parser yields representations which minimize the unknowns allowing us to deal with advanced natural language constructs like anaphora and relativization efficiently. We take advantage of the simplicity of our controlled language to provide as well an easy adaptation to other natural languages than English, with English-like representations as a universal interlingua.