Description logic

Reasoners

FaCT (Fast Classification of Terminologies) is a Description Logic classifier that can also be used for modal logic satisfiability testing. The FaCT system includes two reasoners, one for the logic SHF (ALC augmented with transitive roles, functional roles and a role hierarchy) and the other for the logic SHIQ (SHF augmented with inverse roles and qualified number restrictions), both of which use sound and complete tableaux algorithms. (homepage)
Racer or RacerPro and OWL RACER or RacerPro as it now called was the first (and is probably the fastest) OWL Reasoner on the Market. (homepage)
Pellet is an open-source Java based OWL DL reasoner. (homepage)
Hoolet is an implementation of an OWL-DL reasoner that uses a first order prover. The ontology is translated to collection of axioms (in an obvious way based on the OWL semantics) and this collection of axioms is then given the first order prover Vampire for consistency checking. (hompage)
KrHyper is an automated deduction system for first-order Horn clause logic with default negation (homepage). So it is not a dedicated DL reasoner, but it can be particularly used for DL reasoning, as described in this paper
Jess is not a DL reasoner, aber trotzdem schön ;-)

Protégé is an open-source development environment for ontologies and knowledge-based systems. The Protégé-OWL editor is an extension of Protégé with support for the Web Ontology Language (OWL). (homepage)
Racer dedicated GUIs and IDEs are: RacerPorter, RacerEditor, and Rice (see Racer).