Tetris

Alexey Pajitnov created it in 1984 on a Soviet Electronika 60 computer and accidentally invented the most addictive game in human history. The rules fit on an index card. The gameplay is infinite. Tetris has sold over 520 million copies across every platform ever made — more than any other game. It's been proven to reduce PTSD symptoms, improve brain efficiency, and create a psychological phenomenon literally named the "Tetris Effect." Forty years later, Tetris 99 and Tetris Effect: Connected prove it still hits.