Most air forks will have some way of adjusting the air volume of the positive air chamber of the fork. The positive air volume will affect how quickly the pressure increases when the fork is compressed and therefore how easy the fork is to bottom out. Lowering the air volume will also raise your “dynamic ride height” or how far into the travel your suspension sits, on average, while you are riding. This is different from sag or “static ride height” as your dynamic ride height will change depending on your damping adjustments, air volume, and the terrain that you are riding.
Fox and Rockshox use solid plastic blocks (tokens) that are stackable and attach firmly to the bottom of the top cap of the left fork leg to handle this air volume reduction. Each spacer will take up a set amount of air volume and adding or removing them will change how quickly the air pressure increases and decreases as the fork compresses and extends. This also changes how quickly the fork extends from deep into the travel and can lead to very fast rebound speeds if using a lot of tokens with high pressures.
Many of the small suspension brands (Ohlins, Manitou and EXT for example) use two positive air chambers with a piston between them, one chamber being much larger than the other. Typically you would run the smaller of the two chambers with much higher air pressure than the larger chamber (often around 2x the pressure.) As this smaller chamber has much higher pressure, it will not compress at first until the air pressure in the larger chamber matches the pressure in the smaller chamber. At this point the piston between the two chambers starts to compress slowly which reduces the speed at which the larger chamber ramps up. This system is highly tunable and also does not require any disassembly to change the ramp-up characteristics of the fork. It also can help have a higher dynamic ride height for the fork without having as aggressive of the ramp up at the end of the stroke and the extremely high rebound force that can come with that. The downside of this system is that there are a lot of additional precision parts to manufacture as well as a system that can be more confusing to set up for the user.
Hydraulic bottom outs are starting to become more common on rear shocks, with EXT and Rockshox using them extensively through their range. The only fork that I am aware of that uses one is the Push Nine One, although you can convert (and likely void the warranty of) many forks to a coil spring with a hydraulic bottom out with a kit from either Vorsprung or Push. Hydraulic bottom out circuits are position sensitive (only function in set "area" of the suspension stroke) circuits that only have the job of reducing the occurrences of bottom out events while riding. These circuits add a separate compression valve that is only active for the last 10-25% of your suspension stroke and reduce the speed that your suspension is compressing as it gets closer to bottom out independently of your other suspension valving, giving you a high degree of control over your end stoke without affecting any other damping or spring rate attributes.