First post, by leileilol
All I can think of are destroyed bodies in Doom 3, and maybe the wood/trees in Black & White
Alphatests skips drawing a pixel after an alpha channel's threshold and doesn't carry the sorting issues an alpha blend would have. They're seen on stuff like grates and vents, and can also be used with lightmaps to be shaded while still having holes with depth operations.
But then there's alpha modulation with them, which can potentially lead to interesting effects when done creatively. The thing is, I can't think of many PC games that do to give concrete examples. There's also the possibility of early 3d hardware not being able to do this (not just those not modulating alpha blends). There's some console examples I can think of (Wind Waker), and modern PC game examples that are likely pixel shaders in disguise (like Left4Dead2's gore system for the infected).
It's probably not an important enough specific capability. It's not table fog or paletted texture critical. I'd also prefer replies that do their homework and show an alphatest get modulated somewhere from a game or benchmark from the 96-04 period