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
Too huge: http://hackaday.com/2016/11/28/tiniest-game-boy-hides-in-your-pocket/
Well... pretty hard to beat that ;D
Very nice build but (at least) twice beaten in size ;D:
- https://hackaday.io/project/21453-keymu-open-source-keychain-sized-gaming-console
- http://hackaday.com/2016/11/28/tiniest-game-boy-hides-in-your-pocket/