MenuetOS - New Assembly Based OS (not linux based)
Some rather dedicated people have written a completely new OS in addembly for x86/x64 CPUs that has no basis in Linux/Unix or Windows code.
Because of its use of highly efficient assembly language it is stupendously fast and manages to pack a whole OS with networking, browser, GUI DVD player etc on to a single floppy disk. Obviously it does not have the driver support of either Windows or Linux.
It is designed for applications to be built directly in assembly makeing these also exceptionally fast and small.
I'm not sure about its future given its limited amount of followers and developers so far but if you want to get the absoloute most out of your hardware this OS will probably do the job (assuming drivers and apps appear).