And, for that matter, if a similar boot setup could be created on a more modern computer.
UEFI applications booted from a USB flash drive is pretty close.
Intel produced a command shell and it's possible to write complex applications.
It is a bit limited, the SD card slot in my (extremely cheap) laptop isn't supported by UEFI for instance. I don't think there is printer support etc.
Some motherboards supposedly have the command shell built in, so turning the computer on without any other boot devices will drop to a prompt.
I don't know if anyone has ported
http://www.pagetable.com/?p=48 so that it will run under UEFI (source is here
https://github.com/mist64/cbmbasic).
