UPi is a full-size rack mount for the Raspberry Pi. Though it can apparently accomodate three Pis, it is clearly best if you just put one in, just as depicted in the product photograph. Then, I further reccommend, do not put it in a rack. Just have a single rackmounted Raspberry Pi lying on your desk, the ultimate personal computer.
On Twitter, Foone (patreon) collected this and other increasingly exotic mounting/clustering solutions for the Pi.