3) and the "big" question, open sourceness. I'm not quite sure. Whatever license I put on the code, there'll be n00bs that will be annoying and I'll hate to deal with. Mahalis (whom I respect greatly, he's the GMod Portal SWEP guy) advised me to not release it. I'm a bit 50%/50% on the decision... maybe only over SVN to "filter" n00bs. Maybe nothing. One thing that you'll find for sure, though, is a paper describing all of the techniques used. Including the portals and the rest of the physics, and some of the rendering (lighting through portals which is planned, etc.). There's also tons of Lua to be finished (right now just the portals and "some" physics are Lua-scriptable) which is "open source", of course, and lots of shaders which I'm planning on releasing as "learning resources", especially for Ogre3D users.