Protege
Protege
Protege is a free, open source ontology editor and knowledge-base framework. It was developed by Stanford Medical Informatics at the Stanford University School of Medicine.
The Protege platform supports two main ways of modeling ontologies via the Protege-Frames and Protege-OWL editors. Protege ontologies can be exported into a variety of formats including RDF(S), OWL, and XML Schema.
There is another flavor of Protege which is called Protege Client/Server...
Protege is based on Java, is extensible, and provides a plug-and-play environment that makes it a flexible base for rapid prototyping and application development.
Protege is supported by a strong community of developers and academic, government and corporate users, who are using Protege for knowledge solutions in areas as diverse as biomedicine, intelligence gathering, and corporate modeling.