Piano tuning hammer. It's not a hammer really, but a wrench, I guess because it's hammer-shaped. The setscrew means that it came with interchangeable heads for the different sizes of tuning pins.
Casey

It is something that a steampuker would buy to make into something else. It's worth what you can get for it.

what sombreuil said. if you can find a piano geek, he might want it as a history piece.