G.R.A.D Knife Gun
A very interesting take on bringing a knife to a gun fight, the Global Research and Development (G.R.A.D) Knife Gun houses a small 5 shot revolving cylinder. They were chambered mostly in .22 LR and .22 Short. They were available in different styles, even a bayonet version for the AR-15.
The trigger is in the handle which pops up after you turn a small tab. Simply squeeze the trigger and it will fire like a revolver. Obviously not meant for long range or even accurate shooting, this is meant only close quarters use. One more important note about these guns; the BATFE classifies these as AOW (Any Other Weapons) so this isn’t legal in all states and requires paperwork. Not cheap either, they sell on average for $2,000+ depending on which model it is.