Protégé is available as a desktop application and as a web-based editor. Both are free, open source, and support the OWL 2 Web Ontology Language.

WebProtégé is a web-based ontology editor that supports collaborative viewing and editing of OWL 2 ontologies. There is nothing to install — it runs in your browser.

It supports sharing and permissions, threaded notes and discussions, watches and email notifications, and change tracking with full revision history. Ontologies can be uploaded and downloaded in RDF/XML, Turtle, OWL/XML, OBO, and other formats.

• ✓ OWL 2 and RDF support
• ✓ Collaborative editing with permissions
• ✓ Change tracking and revision history
• ✓ Threaded discussions on ontology terms
• ✓ Multiple upload/download formats
• ✓ Cross compatible with Protégé Desktop

Protégé Desktop is a standalone ontology editor with full support for OWL 2 and direct connections to description logic reasoners like HermiT and Pellet.

It supports editing multiple ontologies in a single workspace, with visualization of ontology structure, explanation of inferences, and refactoring operations such as ontology merging, moving axioms between ontologies, and batch renaming of entities.

• ✓ OWL 2 and RDF support
• ✓ Visualization of ontology structure
• ✓ Ontology refactoring tools
• ✓ Direct interface to reasoners (HermiT, Pellet)
• ✓ Extensible via plug-ins
• ✓ Cross compatible with WebProtégé