I'm thinking this could end up being the Half-Life engine of the Blitz community. Everyone has access to a free SDK with source but not the actual engine source. The graphics are good enough to last a long while for hobbiests, and it gives you the freedom to modify gameplay to the point where it's almost an entirely new game (in other words, a Blitz mod engine).
CShop better be free for owners of CShop 4 :D
CShop better be free for owners of CShop 4 :D