Retro gaming is a massively popular Raspberry Pi application, and while loading your favourite old video games onto an SD card is pretty straightforward, building the physical shell of a gaming system can be daunting for those of us without 3D printers or design skills of any kind. PiBoy Mini bridges that gap by providing partially-assembled devices to their customers. The rest is BYORP: bring your own Raspberry Pi.
They stopped or had severely limited production but I think they have started back up in the last few months.