Protégé is a free, open source ontology editor and knowledge-base framework.

Protégé is based on Java, is extensible, and provides a foundation for customized knowledge-based applications.

Protégé supports Frames, XML Schema, RDF(S) and OWL. It provides a plug-and-play environment that makes it a flexible base for rapid prototyping and application development.

Protégé is supported by a strong community of developers and academic, government and corporate users, who are using Protégé for knowledge solutions in areas as diverse as biomedicine, intelligence gathering, and corporate modeling.