I grabbed this PDF a few days ago: good stuff. Marc has done a remarkable job developing Gambit-C Scheme. I wrote an article for DevX on using Gambit-C for writing small natively compiled command line utilities, simple web services, etc.

Wow, I didn't know Quantz was written in Scheme.

I actually helped beta test the game on Linux, although I didn't end up playing it much after I bought it. Nice to see you can write practical code in Scheme, too.