Some Tools

Graphical Editors

eg, IsaViz (Xerox Research/W3C) or RDF Author (Univ. of Bristol)

RDF Environments (interpreter, etc)

HP Lab's Jena (will also include OWL reasoning soon)

Redland or RDFLib (RDF libraries for Python)

Sesame (RDF Schema based repository and querying facility)

Further info on OWL tools at http://www.w3.org/2001/sw/WebOnt/impls

Validators

for RDF: http://www.w3.org/RDF/Validator/

for OWL: http://owl.bbn.com/validator/ (in development)

Schema registries

eg, EU Cores project (and its possible followers)

Ontology converter (to OWL)

at http://www.mindswap.org/2002/owl.html