You use to see a number of these a few years back. Personally saw one at a Gunshow. There were two complete barreled, 10/22 actions. They looked cheap and jury rigged. I also recall, someone selling a kit to make these up. Other than that, have never shot one nor familiar with anyone who has. ...
There's a dual gun setup, too.
It's made from a commercial kit and two functional Ruger 10-22s.
It uses a hand crank gizmo that operates the triggers in semi auto fashion.
So, it doesn't really look like a Gatlin, more like a twin barreled bench rifle.
Kind of neat, though. http://gatlinguns.net/products.html
There is an actual Gatling, professionally made, but it costs about the price of a late model car. http://gatlingguntheultimate.com/