Patrick Logan says that some Schemers have put a Scheme on the Nintendo DS. Naturally, my first thought was "Hmmm... I wonder if I could do that with XNA?" (Or, more generally, if one could write a self-contained interpreter / compiler that would run on the XBox360). You could certainly do a clunky, self-contained interpreter but the real goal would be something running at chip-level or at least CLR-level. Generating the appropriate bytes is certainly well within the capabilities of the hardware (are you kidding?), but the really, really hard thing would be convincing XNA to start executing your generated bytes as instructions. At the assembly-language or C/C++ level, of course, it's trivial to command the machine to "execute these bytes as instructions," but (one of) the major security-oriented points of managed environments is that such plasticity is forbidden. I suspect that XNA has pretty tight walls around the sandbox to prevent you getting around this limitation, as once you allow this capability, security guarantees become much, much harder. (Not impossible, though, in the case of managed code, since you can still run security checks at load-time -- whether the bytes were generated ten months or ten microseconds ago is irrelevant.)