One of my favorites is an RC boat made out of metal. It turns out that you can get 0.3mm thick, tin plated steel, cut it with scissors, bend it, and solder it together with a normal soldering iron.
Another other one would be a split keyboard, for which I designed and built everything (case, pcb, plate, software) from scratch.
Another other one would be a split keyboard, for which I designed and built everything (case, pcb, plate, software) from scratch.