[pjmlp]

Yes we have. Xerox PARC systems were mainly developed in Mesa after some bootstrap work in BCPL.

ETHZ OS were done in Modula-2, Oberon, Active Oberon.

Olivetti and DEC were using Modula-3.

Several OS were being done in Algol and PL/I dialects back when UNIX was being born.

C's ubiquity is a consequence of UNIX adoption by some successful startups in the workstation market.

If one of the other systems had enjoyed a similar adoption another safer systems programming language would have taken C's adoption.

[illumen]

If Minix had used something else, then Linus probably/might have used that.