TRIPLE is a query and inference layer for RDF. It supports some rather nifty model operatings with intersection and unions. It is a rather different approach to things like Jena's RDQL and others based more around SQL.
It seems a lot like Florid/F-Logic:
It is based on XSB which has:
* Evaluation according to the Well-Founded Semantics through full SLG resolution;
* A compiled HiLog implementation;
* A variety of indexing techniques for asserted code:
* A number of interfaces to other software systems, such a C, Java, Perl and Oracle.
* Extensive pattern matching libraries, which are especially useful for Web applications.