MenuetOS, the 32 and 64 bit assembly platform

"Menuet isn't based on other operating systems, nor has it roots within UNIX or the POSIX standards. The design goal, since the first release in year 2000, has been to remove the extra layers between different parts of an OS, which normally complicate programming and create bugs."

With a user-interface similar to Microsoft Windows, the entire Menuet operating system will fit on a standard, 3.5" 1.4 MB floppy disk. It can also boot from a CD or USB drive.

Source link:
http://www.menuetos.net/index.htm