Tetris

Alexey Pajitnov created Tetris in 1984 on a Soviet Electronika 60 computer, accidentally inventing the most addictive game in human history. The rules fit an index card, yet gameplay is infinite—over 520 million copies sold across every platform, more than any other game. Studies show it reduces PTSD symptoms by 20%, improves brain efficiency by 30%, and created the "Tetris Effect" phenomenon. Outperforms #3's runner-up in accessibility and cognitive impact; forty years later, Tetris 99 and Tetris Effect: Connected prove it still competes with modern titles.