Interestingly, there is modern OS in the same space. That's UEFI. Unti I played with it a few months ago, I thought it was some mysterious firmware-adjacent black-box. But actually it's just an OS, very similar to DOS (though it runs in protected mode).
It has a shell and some basic built-in commands including text editors and such. And most importantly it lets you run executables that a stored on a FAT (well, FAT32) filesystem.
The name BootOS could very well describe UEFI. And equally, a slightly more capable version of BootOS could serve as (very underpowered) UEFI replacement.