Before C was invented there were already other companies writing OSes in high level languages, but yeah thanks to its victory now it gets all the credits.

History is re-written by winners as usual.

I wasn't thinking in terms of winners.

But what were those other OSs and languages? Sounds interesting!

You can start here,

https://en.wikipedia.org/wiki/System_programming_language

https://en.wikipedia.org/wiki/Category:Systems_programming_l...

Some examples, out of my head.

- Burroughs, now being sold as Unisys ClearCase, used ESPOL, later replaced by NEWP, which already used the concept of UNSAFE code blocks;

- IBM used PL/8 for their RISC research, before switching to C, when they decide to go commercial selling RISC hardware for UNIX workstations

- VAX/VMS used Bliss

- Xerox PARC started their research in BCPL, eventually moved to Mesa (later upgraded to Mesa/Cedar), these languages are the inspiration for Wirth's Modula-2 and Oberon languages

- OS/400, nowadays known as IBM i, was developed in PL/S. New code started to be replaced by C++. It was probably the first OS to use a kernel level JIT with a portable bytecode for its executables.

BitSavers and Archive web sites are full of scanned papers and manuals from these and other systems.