Found this today but not sure what it is, appears to be a vise of some sort but for what?

It looks like a old woodworking vise to me.

h-d 4 sure. maybe some kinda mortise jig?

I would lean toward the mortise jig, too, although I note that the shape cut in the metal insert looks remarkably like the shape you would cut out for a single-gang electrical box.  Hmmmm.

Before I saw the underside picture I thought it would work well on the floor - to hold a door while routing out for the hinges.

Then..... i was kind of lost.  Thoughts:

1. It is made to adjust to various widths with adjustment on one side and clamping from the other.
2. The width adjustment could be for whatever it is supposed to clamp, or for adjusting to those jaws.
3. It is very heavy, and those metal jaws don't seem to have a simple way to screw a piece of wood onto.
4. A first I thought that the smooth bore holes were for screwing down to something, but I suspect they may be for aligning a second part to.

My guess is that it mounted clamp side down on a press, and that there was a 2nd half that held a die.
I'm guessing that it is used to punch that shape out of metal?

Swagging again.....

Chilly

if I had to guess, I would think it is used in patternmaking. Everything seems to line up and designed to close with precision rather than with speed.