C:Amie.
Disk on Chip...that's what they use for those pci-card sized 486 embedded systems. Pop it into your pc, and you have another computer running. Woot. DOS.
(Yeah, I would probably save myself a lot of trouble if I just got one of those...
)
I guess it is used for other embedded systems, but I expect most of them to just use compactflash drives and such by now instead.