Serbu Super-Shorty 12 Gauge
The SUPER-SHORTY is based on a Mossberg Maverick (also available on 500 or 590 at additional cost) 12-gauge shotgun which came from the factory with a pistol grip. Because of this, the SUPER-SHORTY is considered an AOW (Any Other Weapon) and can be transferred with a $5 stamp! The gun holds two 2-3/4" or 3" shells in the magazine, plus one in the chamber. The 16.5" overall length, 6.5" barrel and spring-locked foregrip, which pivots out of the way when not in use, make for a very compact package.
Here's the link to their website, and here's a link to a video of the Super-Shorty being fired.
It kinda boggles the mind!
Hat tip to SondraK for this!