A cantilever gate is a sliding gate that doesn't touch the ground. Instead of a ground track and bottom rollers, it hangs off two pairs of top rollers fixed to the receive post. The gate's weight is balanced by a counterweight section that extends past the runout post when the gate is closed.
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.