Some Tools

Graphical Editors

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

RDF Environments (interpreter, etc)

HP Lab's Jena

Redland or RDFLib (RDF libraries for Python)

Sesame (RDF Schema based repository and querying facility)

Validators

eg, http://www.w3.org/RDF/Validator/

Schema registries

eg, EU Cores project (and its possible followups)