A cantilever gate is a sliding gate that does not touch the ground. Instead of a track and bottom wheels, it hangs from two pairs of rollers fixed to the post. A tail past the post balances the gate's weight, so it slides freely with nothing on the ground to jam it.
Cantilever gates win wherever the driveway needs to stay clear: low-clearance vehicles, drainage runs across the path, leaf litter or sand that would jam a ground rail, or just the cleaner aesthetic of no track in the concrete.
The trade-off is steel cost. A cantilever gate uses roughly 30% more material than a tracked sliding gate the same width because of the counterweight tail. The cantilever rail also needs to be a heavier section than a typical bottom rail.
Residential cantilevers usually run 3 to 6 m of clear opening. Commercial cantilevers go to 12 m and beyond, but that's specialised hardware territory.