[Geee]

A differential hoist [0], while not really a pulley system, is a quite interesting simple machine, which can generate infinite mechanical advantage. It has two sprockets which are connected on the same shaft. A chain loops through both of them in opposite directions so that the other wheel is feeding and other is pulling, and the load moves only by the difference of the wheel diameters.

[0] https://en.wikipedia.org/wiki/Differential_pulley

[quickthrowman]

The common/trade name for this is chain fall or chain hoist, and widely used by tradesmen to lift heavy objects when a Lull (material handling forklift) isn’t an option.

[raelming]

Modern chainfalls use one loop of chain to drive a gear reduction which drives a separate load chain. Differential chain hoists with an upper and lower pulley and no gear reduction are found in museums.