Absolutely a turnscrew. I have three long ones, though yours seems to be even longer. I find no makers marks on mine, and one has a split handle that was repaired with rawhide. The handles on mine are different from yours, though. That's a good, comfortable, and pretty handle. I have a smaller turnscrew that was made by Stanley, though these are more common in English examples.
I've wondered about the length. Doesn't seem like something a cabinet maker would need. They are really handy for unscrewing the butt-stock bolts on shotguns and the old two piece stocks of Enfield rifles.
