The dark platform-puzzler Limbo is currently free, for Windows — 100% free to keep — in a limited-time giveaway! Take advantage of it while you can, as Limbo usually costs US$9.99!
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Killer Instinct (2013)
Killer Instinct is a free to play competitive fighting game, the third in the Killer Instinct series, and also its reboot, though some plot elements from the previous installments have been retained. It was released in 2013.