Reader of this Blog propable already read this somewhere else, but it is a really great piece of software and deserves all the publicity it can get:
The AIFB and the FZI Institute at the University of Karlsruhe, in cooperation with ontoprise GmbH, are pleased to announce KAON2 -- a new tool for management of OWL ontologies and reasoning.You can read more at the KAON2 page. There you can also download a free version for non-commercial use (Free as in you supermarket, not the Richard Stallman free)
KAON 2 is mostly the work of Boris Motik, (among other things) an outstanding software engineer and Java programmer. You can meet him (and KAON 2) at the ISWC.