SymbOS
An operating system that is 100000000x faster than all other operating systems in all of the known plains of existence. SymbOS is based on a GUI similar to Windows 95 in look and feel, and plays Pacman, MP3s, video, and Minesweeper, all in multiple instances, at the same time, and at full speed on a CPC, MSX or amstrad PCW with 128k or RAM (not kidding). SymbOS also makes Windows Vista and Mac OS X look planetsized and sluglike by comparison (as if the weren't enough like that already).
If all operating systems were coded like SymbOS, gamers would still be using 386s.