LEGO uses Strain Wave Gearing

And you thought you built complicated Lego systems back in the day? A "great ball contraption (GBC) module" that uses strain wave gearing.

As the creator explains, "I used wave motion of the flex spline to transfer the balls in order to use the strain wave gearing mechanism in GBC module. This differs from the actual strain wave gearing that uses only the reduced rotation of the flex spline as the output." (h/t The Kid Should See This).