Tuxera Systems acquired Datalight in 2019 and now
sells ROM-DOS. They
claim it's still fully compatible with MS-DOS.
Single User ROM-DOS costs $55 USD, and the SDK for building it embedded
is "Call for a Quote".
$55 isn't that bad. If it was a real commercial product with printed manuals, disks,
etc. I would say that is pretty fair. However, I think it is a download only purchase
option though. On the upside it supposedly has built in support for LFN and FAT32....
-Ali