RACER

RACER is Renamed ABox and Concept Expression Reasoner. It is a "a Semantic Web inference engine for developing ontologies, query answering over RDF documents and wrt. specified RDFS/DAML ontologies, and registering permanent queries (e.g., for building a document management system) with notification of new results if available (publish-subscribe facility)" among other things. Its webpage is at http://www.fh-wedel.de/~mo/racer/.

Note that it's available for non-commercial use only, which makes it non-free

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