apparently fun datalog system

The home page for DES does a better job of listing all the features of the system, but it has: Datalog on Prolog, supports SQL, debugging, crazy joins, is super portable, has a GUI, and potentially terrible performance. :-) While I appreciate there are limits to Prolog, Datalog, Kanren, etc., I think declarative approaches are wonderful food for thought, and seeing something with an actual GUI-plus-debugger tickles me pink.