Looks very much like my X-4 torque multiplier, though a larger model.
http://www.x4tool.com/
I have the LW750, and use it with a 1/2" adaptor - that looks the same, but at least a size up. That finial drive after the adaptor is at least 3/4th". They make one that weighs 73lb, and is rated for 12k ftlb output.... so there's lots of options, each one more ******** than the last.
I could be wrong, it could be a swench or something, considering the blacked sockets.
*edit* if you feel the need to own one, there's currently a lot-auction on ebay, with buy it now for 95 dollars after shipping, with a seller who will work with you (and pick you out a nicer one), selling the littlest X-4, it's where I got mine - they look beat up, but they're in great internal shape, mine looked just about unused inside, though I pulled it apart and re-greased it all. It's about 400 bucks off retail, for just some cosmetic wear. Doesn't come with a reaction bar, though - DOES come with an X-4 perfatorque limiter, which is now rebuilt and part of my lugnut rig,