A co-worker picked this up at an estate sale. He has no idea what it is, surprising since he's been a mechanic, a machinist, a welder, etc. The two 'jaws' are opened and closed by rotating the knurled handle. Barely visible at the top of the handle is the stamped word "Brouvellier".
Someone decided that since people are always abusing their adjustable wrenches as hammers,then they may as well make one that looks a bit like a hammer as well.
My atlas lathe has legs that are like cast angle iron. At the foot is a flat plate welded inside the V of the angle iron with a hole in it so you can bolt it to the floor. With this wrench you could use the right side to access the bolt on the left leg and tighten it down. Then move over to the right leg where you can use the left side of the wrench to tighten it down. This way you don't have to be constantly flipping your wrench over to access these different bolts. True, if you sawed off one side so it was like a normal wrench it would be lighter and give a little better clearance in some situations but that's a small trade off for the convenience of never having to flip your wrench over.
Scrolling down the page a bit in the link above to number 286 you find a Double Bit with bits in the handle. That info might lead one to believe this tool holds a bit of some kind and is not for turning bolts and nuts. ??
Pretty sure that is called a French Key, just an alternative form of an adjustable wrench. I seem to recall a similar thread awhile back where someone came across this and an European member clued us in.
My buddy has one of those. He swiped it out of a Russian tank's tool kit when he was in the Yugoslavian military.
It's essentially an adjustable wrench, but you can really tighten the jaws by turning the handle so it grips like a vise. It's pretty solid, so you can then hit it with a hammer to get whatever it's gripped onto moving.