The Gilboa Snake is an Israeli rifle (from the same designer behind the Cornershot) that essentially combines two standard ARs into a single unit. In its civilian configuration it has two of every part - barrels, bolts (mirrored, so one ejects left and the other right), triggers, buffers, etc. In its military setup, the triggers and recoil system are combined into single units, and this makes the gun arguably practical. With a single trigger, a person fires two rounds simultaneously, resulting in either two simultaneous hits at close range, or the potential for one hit at longer range instead of what might be a miss with a regular rifle. This is a concept that has been experimented with by pretty much all major militaries over the past decades; the Russians, French, and Americans all had rifles like this. Other approaches to the end result included duplex and triplex ammunition (multiple bullets in one case) and hyper-burst firing mechanisms (like the Russian AN-94 and German G11). Ultimately all of the different systems were deemed poor compromises compared to normal rifles, but it's not as bizarre of an idea as it might first appear.

Unfortunately, the civilian Snake has to have two separate triggers to avoid machine gun classification in the US. It's difficult to fire both triggers simultaneously, and this limits the practical military applications of the gun.

Oh, and don't miss the unique elements in the Snake to allow for the barrels to be zeroed before mounting sights!