A capstan or "Cathead".
http://www.littlehercules.com/catheads.html
A capstan or cathead has a constant RPM, these days supplied by electric or air motors, in times past by steam engines. Several loops of rope are whipped around it, and pulling on the end of the rope causes more friction, and allows the spinning capstan to pull the load on the other end of the rope.
Releasing tension on the end of the rope loosens the rope around the capstan and allows the capstan to slip inside the rope. The load can be let out in a controlled manner by maintaining and releasing tension on the end of the rope.
The rounded smaller upper rim is to allow a rope to be looped around it quickly and easily without snagging. The larger lower rim is to help keep it from slipping down and under, wrapping itself on the shaft beneath when slack is let out.
Possible sources: Forestry (moving logs around), farms (attached to tractor PTO), ships or dockside, by railroad sidings to move cars up to the loading dock at an industry or warehouse, tugging pallets and crates around warehouses, etc.