- AKT Reference Ontologies - Various ontologies developed in the framework of the Advanced Knowledge Technologies project. Includes a portal ontology.
- Business Process Management Ontology - BPMO is an integrated information model including business process design, project management, requirements management, and business performance management.
- DAML Ontology Library - An index of more than 200 publicly available ontologies expressed in DAML.
- Descriptive Ontology for Linguistic and Cognitive Engineering - DOLCE is the first module of the WonderWeb Foundational Ontologies Library (WFOL).
- National Cancer Institute Thesaurus - An OWL translation of the NCI Thesaurus, available for download (32 Mb) or online viewing.
- Open Biological Ontologies - Provides access to controlled vocabularies for shared use across different domains, like MESH and Gene Ontology.
- OpenCyc - OpenCyc is the open source version of the Cyc technology, the world's largest and most complete general knowledge base and commonsense reasoning engine.
- OWL Ontology Library - A selection of OWL ontologies usable in Protégé.
- Semantic Web for Earth and Environmental Terminology - Several ontologies published by the Jet Propulsion Laboratory in OWL format. Includes Space, Units, Earth Realms, Phenomena, Physical Properties, Substances and Units.
- Suggested Upper Merged Ontology - A free, formal ontology in first order logic with domain ontologies totalling 20,000 concepts and 60,000 axioms, with mappings to all of WordNet.
- SWETO DBLP Computer Science Bibliography - Semantic Web Technology Evaluation Ontology referencing printed journals and proceedings. Data from DBLP, DataBase Systems and Logic Programming, maintained by Michael Ley.
- The Enterprise Ontology - Collection of terms and definitions relevant to business enterprises. Developed in the Enterprise Project by the Artificial Intelligence Applications Institute at the University of Edinburgh.
