Here's something I didn't know existed.
Behold, the rocket monocopter!
It's a wing on one side, and a rocket pointing horizontally on the other.
Or, in the case of this monstrous one...
...two J engines and a K in succession, as this spinning surfboard wanders the sky looking for heads to lop off.
It's apparently possible for these things to get themselves into a nice flat autorotation spin on the way down, too, so you don't need a parachute.
Well, that's the theory, anyway.
One-bladed propellers are actually very desirable, essentially because the more blades you have, the more turbulence each blade must cope with from the blades in front of it.
The obvious problem with dropping to one blade is that if it's mounted on a shaft and developing thrust, then that thrust will be off-centre, spinning around the shaft with the blade, and thus ruining the shaft bearings quite quickly. So you only see single-bladed props in oddball applications like these monocopters, and extremely tweaky ultra-speed control-line models, and certain rather expensive ceiling fans.
There are also propeller-driven monocopters, where a motor and prop takes the place of the rocket in the above contraptions. With modern digital control and image-processing systems, monocopters may be useful as unmanned aerial vehicles: