Updated: Sept 24 2008: more links, RAP

A very thin category at the moment, but the new Drupal Rules project may help to fill it out.

The RAP project has a simple forward and backward chaining inference engine using networks of relationships rather than condition/action statements like a true rule engine.

There is also a simple and probably quick Prolog backchaining engine implemented in PHP that might be useful for relational RDF-stytle inferencing. See link below.