Arduino-Boy
A primitive handheld console with an 8x8 display and 4 buttons I designed, built and programmed myself.
It runs on an Arduino Micro and has an operating system that allows to have multiple programs (for example games) between which you can switch as you like.
There are 3 programs I already programmed for it: Snake, Paint and Break-Out.
If you download the code from github you can also easily add your own programs.