A self-closing hinge has a spring (cheap) or a hydraulic cartridge (more controlled) that returns the gate to closed every time it's released. The Australian Standard AS1926.1 mandates self-closing on every pool-barrier gate, from any open position back to fully latched, with no manual help.
The two dominant brands in Australia are D&D Technologies (TruClose) and Locinox (Tiger and Mammoth ranges). TruClose hinges are tension-adjustable and rated to 30 to 70 kg per pair depending on model. Hydraulic gate closers handle heavier leaves but cost more and need annual service.
Tension setting matters. Too light and the latch doesn't engage. Too heavy and the gate slams hard enough to crack a fingertip. Aim for a controlled close in 2 to 4 seconds.