So it's a tie score. KOSCIELSKI'S & K.G.S. in Minneapolis MN has unveiled a credit card sized shotgun. Actually it's a muzzleloader that uses BB's as the shot. The device is approximately the length and height of a credit card, but is considerably thicker,
For ingenuity I'd like to applaud these folks for building a unique mousetrap. Of course with the bevy of .380 auto pocket pistols for when you can't carry a real gun, I wouldn't know how this fits into someone's choices of what to carry.
For the potential of this device to fail at the most inopportune time is too great for me to consider owning one of these. The trigger system is electrically operated, so some kind of power source is required. You have to push a button to fire this device. Again, button can break or be accidentally pushed. Finally I assume this device would ride in someone's back pocket. Sitting on this item all day long week after week can't be good.
More power to them if they sell these things. Good luck.