No, it's not what you're thinking. This game, which shares its name with Valve's classic 2007 title, was a text-driven interactive novel and game about an astronaut who returns to Earth only to find that all signs of civilization have vanished. After finding an open computer network, the player must use clues hidden inside various computers to piece together what happened to his fellow homo sapiens. Sure, this would be a long-winded way of telling a story nowadays, but the premise is quite solid and—back then, at least—books were made out of paper and real ink, so this was innovation at its finest.