Gameboy, Gameboy Color and possibly Gamboy Advanced modular cartridge cases.

I printed out the full set of parts for version 2.3 of my Gameboy cartridge modular case and snapped everything together last night.
The cartridge pieces work perfect and everything fits together nice and snug, though the new frame pieces I added in version 2.3 need a slit bit of work.

Check out the forums for further details