I don't know how good French gamer Kotomi is at actual gaming, but when it comes to case mods I'm impressed. Taking an original Super Mario Brothers cartridge, the stripped down guts of a "NES on a chip" clone system was squeezed inside, making for one of the most compact (and cool) NES systems I've seen. It's all functional too, with the obvious cartridge slot, power and reset buttons together with composite video, stereo audio and not one but two joystick ports.
Even though the clone system used was much smaller than an original NES console, it still required some Dremel work and soldering iron action to get it flat enough for the cartridge's small dimensions. Kotomi is calling it the ideal system for taking to friends or on vacation. I bet he'd make a killing selling them, if he could justify hacking original cartridges.
Actually, don't be surprised if you see replica cartridges packed full of NES goodness soon. This looks like the sort of thing unofficial system cloners would jump on.