Franklin Arms gen 3 binary 3 position trigger. I've only fired about 100-150 rounds it it. Trigger assembly kit only, lower sold separately. With fit and AR lower receiver. This is not a full auto sear, binary triggers for once on pull and one on release. 

I paid $300, they are on sale now for $200.
This is from Franklin Arms:

The Binary Firing System® GEN 3 (BFSIII®) is a 3-position trigger. In position 3 it fires one round on pull and one round on release, making this trigger ideal for both tactical and competition use. The BFSIII® provides greatly reduced split times between rounds, allowing for tighter groups. The AR-Essential trigger comes with just the essential trigger components needed to install the Binary Trigger into your AR. This makes the AR-Essential trigger a cost effective trigger option.