The difference is intervention: a forklift proximity warning system only alerts the operator or pedestrian when a person or object is within a set distance, while a collision avoidance system also judges risk from distance, direction and speed and can act on the truck, for example by reducing speed on compatible forklifts. Warning systems rely entirely on a person noticing the alert and reacting in time. Avoidance systems reduce that dependence but need a speed-control interface on the truck, which not every make, model or age of forklift has.
The full page is forklift collision avoidance systems. Some products marketed as collision avoidance only warn, so ask exactly what the system does to the truck, under what conditions and on which models. Check whether intervention is staged, with a warning before any slowdown, and whether operators can override it. Both types log events, which helps locate near-miss hotspots. OSHA 1910.178 requires neither. For a plain comparison of warning methods, see proximity alert systems, and for the tag-based approach see proximity detection.