The 3DO! Lots of companies that made it big on later systems like the PlayStation and Saturn got their start developing 3DO games. Examples:
Solar Eclipse = Saturn
Total Eclipse = 3DO
Enemy Zero = Saturn
D = 3DO
I would also suggest Sega CD (think: Out of This World, Heart of the Alien, the Lunar games, the masterpiece that is Sewer Shark ( ;) ), etc.!), as some others have, but I would definitely say that it's been less forgotten than the 3DO.