搜了一下:
http://www.zebor.com/main/zdos.html
ZDOS is a 32-bit real time OS for the X86 CPU family, written entirely in assembly language for maximum performance.
ZDOS was developed as a 32-bit replacement of 16-bit DOS, but with modern features like multi tasking, demand paging, SMP etc..
As a BIOS vendor we also integrated a complete 32-bit BIOS within ZDOS, in order to restore the power users had in the old, good DOS days.
With ZDOS you can do every thing you used to do, but now in a full 32-bit, multitasking environment. You can create 32-bit, multi tasking processes with a lot of threads, invoking safe reentrant 32-bit BIOS and DOS API calls.