It is called various things be we call it "power push" in NZ but it is called by different names overseas. It has four rollers that grip the main wheels and then turns them. When the push is complete the pilot parks the brakes, and the unit retracts the front rollers and the aircraft can taxi away or the ground engineer can drive the unit away. The pilot steers with the tiller at the command of the ground engineer, and the ground engineer remotely controls the unit.
It works very well and is very capable and works well.