A pea sheller is a machine that automates getting peas out of their pods. It can save the hours of manual work required to reduce several bushels of peas in the pod down to two small bowls.
The machines are not just for English garden peas. They can be used for field peas, black-eyed peas, lima beans, etc.
They can be electric, or operated manually with a hand crank. In the 1930s, pea shellers appeared that you attached to a stand mixer, with the axis of the mixer powering the machine.
The general idea with all pea shellers seems to be that the pods get fed through rubber rollers, which squeezes them just enough to make the peas pop out, without squishing the peas.
Some people make their own from old wringer-washers.
Commercial ones can spew out upwards of 500 kg (1100 pounds) of shelled peas per hour.
They are seldom used in homes anymore because people buy their peas already shelled now, either frozen or canned.