Ontology sites

There are a number of systems and formalisms that can be used to develop a knowledge base (KB) for an intelligent agent. For instance, agents that interact with humans will need some modeling of "common sense": the human's general knowledge of the world.

Ontolingua (Stanford) Web-based editor, consistency checker etc. for ontologies. Supports group-based ontology development. Many export formats (Prolog, Clips etc.). Example of a KB describing 'time', exported from Ontolingua in Lisp format.
LOOM (USC) Another powerful system, includes an inference engine, contrary to Ontolingua. History and explanatory text . These systems are usually heavy weight, in Common Lisp, requiring substantial resources. However, new developments are towards C++ or Java-based implementations (PowerLoom).
CYC Project and company by D. Lenat. Part of their world-knowledge bases will be made freely available ( OpenCYC).

L. Schomaker