I found this little os that is still in alpha stage and tested it under vmware. The GUI is a copy of the one from Beos. The kernel is only 98kb. I don't have the slightest clue what file system it uses. Only thing I know is that it's not posix compatible. Another similarity to haiku is that when it boots the first thing u see is the terminal.

This is the homepage : http://monaos.org/about.html [1]