From Dust and Insanely Twisted Shadow Planet are both part of Microsoft's Summer of Arcade Games promotion for the Xbox 360. Neither is supposed to be out, but for some reason, both now are.
This isn't that big a deal when it comes to From Dust, which depending on where you are in the world will be out in a few hours' time, but ITSP wasn't due until next week, so that's a genuine head start on proceedings.
Both are available from the online version of the Microsoft Store.
UPDATE - Aaannnddd Microsoft shut the gate! They're no longer available. Sorry everyone, you'll just have to wait until they're actually released.
Insanely Twisted Shadow Planet [Microsoft]
From Dust [Microsoft]
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