We've seen Gameboy mods before, but I didn't know you could repurpose one to act as a guitar effects and sample loop box. That's just what software Nanoloop does, and since you don't really want to be jabbing at a D-pad while you're meant to be concentrating on your frets, Joey Mariano has just the breakout-box hack necessary. Edit: Check out Joey's clarification of the setup in the comments.
Check out the video of the system in action after the cut
The Gameboy itself undergoes some drastic surgery, with the battery compartment removed and various wires hooked up to the circuitboard's button traces. They terminate on a DB-15 serial port, which links up to a custom breakout box; mains power routed through there keeps the Gameboy going, while it also has sockets to plug in standard sustain pedals to control the handheld.
What you end up with is a way to trigger all manner of loops, samples, effects and even macros without interrupting your playing. Nanoloop is Gameboy sequencing software, and the pedals mean you can trigger loops while still playing. Check out Joey's video below to see how it all comes together.