I have been using Kowari for a while. I am quite happy with it, but I am planning to ditch it in favor of the new release of Mulgara (Open Source for of Kowari) lead by Paul Gearon. If you haven’t check it out yet, take a look at it because is more than worth it. I have also been exploring other options. There is modified implementation of SPARQL for MySQL maintained by Eric Prud’hommeaux, his approach is very interesting one if you rely on MySQL server, it is a must. You can find some of his related papers and presentations and here. The last one I ran into recently is the RDF store implementation by Oracle Spatial. I have not played with it much, but it has Oracle behind, and that is a big name…