An ATTiny85 game system with swappable game by changing the cartridge
Smaller than the size of a credit card.

Running at 16MHz and with only 8Kb of memory to fit everything into it is really tiny too. The cpu is soldered on the game cartridge and the game is uploaded in the chip.

The 3D printed case can be found on TinkerCad (see link further down)

The Schematic used is based on the great work of Billy Cheung ( https://github.com/cheungbx/gametiny )
Except in this case i put the ATTiny85 on a separate tiny cartridge PCB with each pin of the ATTiny broke out to a 8 pin header. I made several of the cartridges and programmed them with one game. The so called 'Gametiny' games can be found on several sites but there are a fair among available on the provide link.