I though when I first looked at the pictures it was one of those tools to put set in a hand saw. But with the flat spring on top I believe it is a hand crimp of some type for sheet metal. The one gizmo that looked similar was floor mounted and foot operated. It put a dimple in a sheet metal seam rather than use a rivet or screw.
If there was no spring on top I would say it was a notcher for sheet metal.