Iptools---you got me going in the right direction, it is a Waller Tool Co. butt mortiser. Now, if anyone needs their butt mortised this tool might do the job. Looking closely at it I suppose it might be used on hinges, the old square type. Depending on the length of the hinge you would have to move it for a second mortise. So, what do you think it was mainly made to do? It appears to be fairly rare.