>>luke2m+(OP)
KolibriOS is an open-source Operating System for x86 (32-bit, 586-class and above). It is entirely written in assembly (assembled with FASM). It requires only 8MB of RAM to boot. It has a TCP/IP stack and USB support. It has a graphical user interface which is actually on par with most of the "lightweight" Linux window managers, such as LXDE (but I think LXDE is probably larger than this entire OS lol). It fits on a single floppy.