World of Warcraft
Half-Life 2
Correct Answer: Minecraft

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Created by Markus "Notch" Persson and released as developmental build in May 2009, Minecraft sold its first million copies by January 2011, less than a month after entering its beta phase in December. By 2016, the sandbox building sensation sold over 106 million copies (25 million on PC) to become the world's best-selling PC game and the second best-selling game on all platforms worldwide, second to only Tetris which has sold around 500 million copies since emerging in 1984.

Interestingly, Wii Sports follows Tetris at 82 million, in case you forgot just how successful Nintendo was with that platform. World of Warcraft, Diablo III, Counter-Strike and The Sims round out the list of top five best-selling PC games, all having sold well over 10 million copies.