This is the official site of the former KPB Engine. Nowadays, it is not an engine anymore but as far as I know for architects and stuff like that:
http://www.kpb.com/
A very early version of KPB Engine was used for creating an old abandoned game called Unbirth, made almost entirely from Tomas Grip. The game was going to be free but Thomas abandoned it due to technical problems mainly. It's spirit lives in Penumbra games and especially at the 2006 Tech Demo. The new main site for Unbirth is this:
http://unbirth.frictionalgames.com/