Some of the top-end telescope mounts use harmonic drives instead of the old worm and wheel.Ken I said:...
For all that harmonic drives are fairly commonplace, few people know what they are or how they work.
I use them all the time in my line of work - robotics.
Cyclo gearboxes are even wierder.
These devices provide reductions between 50-300 : 1 at better than 50% efficiency - which makes them reversible !