[snvzz]

Tangentially related, DOS is a popular choice in this category of hardware.

Freedos has released 1.4rc1 recently, thus 1.4 is close.

Svardos switched to EDR-DOS kernel, which is derived from DR-DOS. That's a very nice kernel, written in assembly. Notably, Windows 3.1 works with it, including protected mode.

[lproven]

Yup. I wrote about it:

https://www.theregister.com/2024/12/23/svardos_drdos_reborn/

I have built a hobby project around it:

https://github.com/lproven/usb-dos