Does anyone know what this piece of machinery is/does?
No idea, but I am answering so I can re-locate this question later in case someone else knows, as I am curious, too.
Looks like a fence tightener to me. The pulley with the chain stops is the working pulley and the cable pulley is the tightener. Just pull on the chain and the cable is pulled at the same rate, thereby tightening the cable on the fence. Just a guess though.
