We've mentioned the Raspberry Pi before, a budget micro-computer that's gone through multiple iterations - its low price (typically $50 or under) means it's a wonderful educational tool or, alternatively, a side-project for enthusiasts. The Game Boy Zero is an example of the latter.
As the name suggests this is a Game Boy fitted with a Raspberry Pi Zero board - pictured below, it's the work of a certain 'wermy'.
Wermy has taken a Game Boy and added a new colour screen, and then heavily customised the Pi to operate within the casing. Two additional face buttons (from a NES controller) have been added, in addition to neat buttons on the back that work as Z and L.
The purpose of this is to run a Raspberry Pi-based emulator - with the inevitable grey areas that entails - through the system, but the neat touch is that Wermy has also created a Game Boy cartridge that's home to his micro-SD card; the whole thing is designed so that the cartridge goes in the original slot for that classic feel. Naturally the emulator plays an array of retro games - let's be generous and assume Wermy is downloading games he owns.
You can see it in action below.