What is this pulley-ish thing?

My lady friend dug out this old piece of gear she's had for ages, and she doesn't remember what it is or where she got it. Upside down it acts as a progress capture pulley. Right side up it feeds both ways. I have no idea what's going on with the little dongle at the top. I'm for sure not the smrtest man in the world, but this strikes me as a weird-ass object. Anyone know what the heck it's called and what it's used for?

Looks suspicipusly like a beal monitor ? Fall arrest/work positioning for industrial rope access.

Looks like one of these - http://www.verticalmuseum.com/VerticalDevicesPage/Misc/RopeGrabsRockerArm.php 

This is identical to a Yates Rocker that I got about 20 years ago. See here for photos and description:
Yates Rocker

I used, and occasionally still use, mine for TR self-belay. It’s a bit spooky. It slides up the rope very easily, but it also slides down the rope very easily. If I’m gripped and slide it up above me and glance away, it slides back down to below my harness. I really need to use a neck cord to hold it up but have been too lazy to implement this for the last 20 years.

This device is similar to the much older Hiebler ascender:
Hiebler Ascender
which was designed in part to work on icy ropes. I had one of these in the mid 70s. It was very scary, because it could easily twist completely off the rope. Mine was the newer model that has the “safety clip” which was pretty worthless.

These devices when loaded put a S bend in the rope which is what holds you.

On the Yates and Climb-X and others the pivoting tab controls how far apart the two arms can open and thus controls how freely the device slides up (and down) the rope.

One caution if you use it as an ascender. Because it grabs the rope by putting a little S bend in it, it will not grab a taut rope. So if, for example you have fallen off an overhang and are hanging on the rope, the device can NOT be placed on the rope above you i.e. to ascend back up. A Tibloc or other lightweight rope grab device is a better choice for that, and I know folks who keep one on the back of their harness for just such a situation.  (Of course there's no reason to carry any hardware for this if you have a sling or loop of supple cord.)

I use a clone of the CAMP Lift as my TR solo backup device. It really does move easily up the rope. And down it, if you're not loading it downwards with the carabiner.

Sick, thanks for the info, guys. I'm not planning on using it for anything, I was just curious.