Doom (1993)

id Software didn't just create a game — they created a genre, a modding culture, and the multiplayer FPS. John Carmack's engine was so revolutionary that "Doom clone" was the genre name before "first-person shooter" took over. The level design is non-linear and rewards exploration. The shotgun is the most satisfying weapon in gaming history. The modding community has been making WADs for 30 years and shows no sign of stopping. Doom runs on everything — literally everything, including pregnancy tests and ATMs.