No idea if this would work or be practical, or if it has been done before or patented. Basically, air is constantly coming in. Water comes in the hole until it floats the float ball up. Air pressure builds and pushes water out until it empties and the remaining air leaves the same way the water went. Without air pressure, water pushes the ball back down and the take begins to fill. During the time the tank is filling incoming air is escaping via the water inlet. So the slower the air inflow, the more efficient it gets.
Should someone put a valve and block the exit, the whole thing just pauses. No damage is done, no air is lost, meaning it might be useful for hand-pumped applications in remote areas of at construction sites or what have you because it's easy to shut off.
It might also be useful for small decorative fountains wherever you might want a lot of fountains cheaply. There's only one moving part and no electricity, plus it has a built in pulsing action that might make it more interesting. Not sure how to even out the flow without adding complexity though.