Datalight ROM-DOS
Flash file systems and flash memory systems by datalight
http://www.datalight.com/
FreeDOS
Freedos is a complete, free, 100% ms-dos compatible operating system. works on old hardware, in dos emulators, and in embedded systems.
http://www.freedos.org/
PTS-DOS 2000
Phystechsoft www-site
http://www.phystechsoft.com/ptsdos/