BugOSAn impressive OS project for a single author. The command line functionality is reminiscent of DOS, but it runs any number of simultaneous virtual machines, and has lots of network apps, games, and utilities. It includes C, Pascal, and an assembler. It is even ip6 aware. All of this, on two floppies.
Unfortunately, it is poorly documented. Maybe a technical author with some knowledge of Hungarian can help the rest of the world better understand this gem.
See http://bugos.nop.hu; I have regrettably found no other references for it.