I've posted a few months ago about Piggy Bank, without clearly stating it is but one of the various tools developed by the Simile Project, Semantic Interoperability of Metadata and Information in unLike Environments. All RDF-based stuff, but user-friendly, a qualifier which does not come to mind when looking at some other RDF tools (no names, please). Have a look at Longwell browser, for example. You can try it on-line to find your way through W3C specifications. Local installation requires a bit of Java logistics, not tried it yet.
What people say about what they do is also interesting stuff. I had mentioned Stefano's Lynotype before. Posts are not frequent, but always thoughtful. See e.g. Data First vs. Structure first.