Differential
Differentials sum input speeds, allowing for the creation of rotary calculators
Coaxial Cogwheel
Although this appears to be an impossible setup at first glance, it is enabled by the Coaxial Cogwheel
Planetary Gearset
Planetary Gearset's Shafts rotate twice as fast and the opposite direction to their teeth
Double Cardan Shaft
An aesthetic alternative to the Gearbox for getting Shafts to turn corners