purely for the sake of vanity (ok, maybe a bit of humour as well <g>) here is a single sector operating system written for a small contest

It's somewhat broken in that it refuses to load the file system past the second sector correctly, but hey

You might need bochs to run this. I developed it with bochs, and haven't ever really tested it when written onto a real disk and booted up with a regular system... but that should work too.

Enjoy the power of POS

Oh yeah, you might also need some documentation besides the source code:

c - clear the screen
l - list files inside the fs
d - dump file contents to screen
e - execute file (only file executable in this is test)
s - shutdown (hang)