When a uni department replaced all their Macs, I got my hands on a power Mac G4 Cube (yes, one of those that sits in the MoMA). I haven't been able to fix it (something's fried) but I plan to keep the shell and most of the innards as well as the awesome take-out mechanism and add an RPi or something else inside. Passively cooled and beautiful enough to display in the living room...