Gameboys are great fun for hacking on. There are open
source development
 kits and languages out, the hardware is *very* well documented, and there
 are tons of third party expansion and adapter cards. 
[...]
Elektor magazine published a design (alas without the source code to the
firmware) for an audio-bandwidth digial storage 'scope card for the
Gameboy. No, I am not joking...
-tony