Hackaday.io member Peter Barker (aka "Moosepr") has used a Raspberry Pi Zero to make a tiny GameBoy-style handheld console that runs RetroPie games. It is so small that it is actually smaller than an original GameBoy cartridge.
http://www.notebookcheck.net/Raspberry-Pi-Zero-used-to-make-possibly-world-s-smallest-GameBoy.203000.0.html