I think I had heard of this years ago, but I really ran across it in Ghost in the Shell. (Togusa, one of characters, carries it as a weapon of choice.) Chambered for .357 magnum and .44 magnum, it seems like a very cool weapon.
The Unica functions as follows: The first triggerpull is a normal double action pull, it cocks the hammer, and then releases it, firing the gun. Upon firing the upper part of the frame recoils. This movement then cocks the hammer, and automatically rotates the cylinder. When the upper frame has completely recoiled, it is pushed forward again by a spring. When it has returned to its forward position the gun is ready to fire another shot, only this time a light pull in Single-Action mode, as the hammer is already cocked and the cylinder rotated.The barrel is aligned with the bottom of cylinder, not the top as is usual in revolvers. It is supposed to be very accurate.
Unfortunately it isn't listed on the Mateba website anymore so I guess they stopped making them.