Back when I was in college (2001-2002), a friend of mine showed me an operating system that boots off a stiffy disk. Now I know you get single-stiffy-disk sized linux distros, but this isn't a command-line operating system... it has a full colour interface, with transparency, can run multiple applications, etc.

Anyway, at the time it was rather impressive. So I decided to Google it the other day, and found that the project's still going (and it's still only 1 stiffy disk big), and has had lots of extra functionality added. It may not have much practical use, but it's worth checking out.

(from the site) "MenuetOS is an Operating System in development for the PC written entirely in 32/64 bit assembly language, and released under the License. It supports 32/64 bit x86 assembly programming for smaller, faster and less resource hungry applications."

Link: MenuetOS