A ROM-DOS is an embedded operating system designed to allow DOS applications to run on embedded hardware.
Programmers can develop and begin testing applications on standard desktop computers running MS-DOS. Then they can copy the application to the embedded system running ROM-DOS.
Because ROM-DOS is designed to boot off solid-state ROM, it allows embedded systems to be nearly "instant on", compared to booting from a floppy disk or a hard drive which are much slower.
Many PC/104 computers run ROM-DOS*. At least one digital camera runs ROM-DOS*.