Is it just / ?
I kid. But really, besides “its all a file”, if you take away the gui, is the only difference the syntax ? How libraries interact? How disks are mounted ?
If we stripped all ms’s junk out and made windows open source, would we still prefer linux?
When you get to a very basic level, is one of them more efficiently coded?
OpenVMS is still semi-maintained. It’s DEC’s old operating system that Windows NT draws some inspiration from because Microsoft hired a bunch of ex-DEC engineers.
There’s also 9front, a fork of Bell Labs’ Plan9.
Wegmans’ checkout uses Toshiba 4690 OS, which I think is vaguely descended from CP/M.
I think IBM still maintains their i operating system, which used to be called OS/400.
Network equipment like enterprise routers and switches tend to run weird unique things, Cisco equipment runs IOS and Adtran equipment runs AOS.
Oh man a stew of them. Nice