Tetris

Tetris, designed by Alexey Pajitnov in 1984, stands as a monumental achievement in video game design. Its deceptively simple rules, involving fitting falling blocks together to clear lines, have ensured its enduring appeal and remarkable replayability. The game has been released on nearly every gaming platform imaginable. As of 2014, the mobile version alone had sold an estimated 425 million paid downloads, making Tetris one of the best-selling video game franchises of all time. The game's increasing difficulty, often marked by faster drop speeds at higher levels, provides a consistent challenge that has captivated players for decades.