JADE the Java Agent DEvelopment Framework. Middleware that follows the FIPA (Foundation for Intelligent Physical Agents) specs. An RDF codec for JADE has been available for a year or so, but I can't find any recent developments in this direction.

Also from Parma University amongst quite a lot of other interesting things COMMA (Corporate Memory Management through Agents) - merging multi-agent systems, XML, RDF formats, machine learning techniques.