I don't think one person here has mentioned GamersGate.
Which is weird, because they're the closest thing to a challenge for Steam right now. They gained steam (no pun etc.) by releasing some of the same games as Steam, except without DRM that came with the Steam release, which also means you can play them offline with no hassle. So they've gained a growing market without having games pulled from Steam (not that they could get that, but that's not the point). They also do the whole ridiculously priced sales thing.
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Ace Detective in Sir Chris' Police
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