Traditionally, circumcisions were performed with a knife, or, in more primitive societies, with a sharp stone. The foreskin was stretched out and sliced off. In more modern times standard surgical tools became commonly used.
Currently, there are some devices which consist of a pair of plastic tubes where one is fitted inside the foreskin and the other is snapped over the outside, both cutting the skin and pinching the blood vessels to stop the bleeding. The device is left attached until the skin heals and it falls off on its own.