Create Ontologies with Protégé
Protégé is a free, open-source platform that provides a suite of tools to construct domain-specific models and knowledge-based applications with ontologies specified in OWL2. Protégé provides two tools: WebProtégé and Protégé Desktop. The former is a web-based environment that enables collaboration on creating ontologies. The latter is a desktop environment for creating ontologies and reasoning on them with description logic reasoners like Pellet.
Create Ontologies with Jena
Jena is A free and open source Java framework for building Semantic Web and Linked Data applications. Jena provides Java API to create Resource Description Framework (RDF) graphs and query them with SPARQL. It also provides Java API to work with RDFS and OWL2 vocabulary to add extra semantics to the RDF graphs. Finally, it allows persisting RDF graphs in TDB, a native high performance triple store and exposing them as a SPARQL end-point accessible over HTTP. Fuseki provides REST-style interaction with the RDF graph.
Reason on Ontologies with Pellet
Pellet is an open-source Java based OWL 2 reasoner. It can be used in conjunction with both Protégé and Jena. Pellet includes support for OWL2 profiles including OWL2 DL. It incorporates optimizations for nominals, conjunctive query answering, and incremental reasoning.