This is a tool for cutting perfect 45° bevels in 6mm Depron/foamboard. It uses a regular shaving razor, which you insert in the slot.
Place the tool on the edge of the Depron, slide along and you'll get a single perfect slice of Depron with what's left being cut at exactly 45°.
OnShape link for remixing:
Print positioned with the handle to the side and the top edge on the bottom. No supports needed, at least on my printer.
The author hasn't provided the model origin yet.