QuOnto

QuOnto is a Java-based reasoner for the description logic DL-lite with GCIs, which is a sublanguage of OWL DL that can be treated with very efficient database techniques. QuOnto implements a query rewriting algorithm for both consistency checking and query answering for unions of conjunctive queries over DL-Lite knowledge bases.

The system is not available online, but can only be retrieved for "testing purposes" by directly contacting the authors (which is why it is classified as a prototype here – it apparently has not been applied in many practical scenarious yet).