Just in case you're serious, this is in fact a tool for driving metal fence posts like round posts for a chain link fence or t posts for a garden/cattle fence. You slide it over the post and drive it down to hammer in the post. Way easier and safer than using a sledge.
Huh TIL. I've put up many posts, used post hole diggers and augers of various kinds. Never saw anything like this. The soil where I live has lots of clay, this device looks futile