I'd seen something like this before, but skipped over it at the time since my interest in ARs was low.
It's an AR that takes AK magazines. At first glance it seems silly - AK magazines are more expensive, heavier, and the release isn't as convenient.
This morning I realized one reason you might want to go that route - from what I've read, cutting the magazine well out of a 0% lower can be a big deal for people with limited equipment. The opening for an AK magazine is much shallower.
An AK magazine would also be convenient if you were doing a 7.62x39 conversion, or if you wanted to use an inexpensive steel drum.