I've had a couple of people think it may be an ice cutter or chopper. I did think when I first seen it that it may be a circle cutter or at least a scriber maybe even a shop made tool.
I've seen something similar called edge dividers. The flat section slides along the end of the board, the scribe is set to a distance to lay a mark parallel to the edge. This one is JUST a little nicer. EDGE DIVIDERS