Mac OS 9 was written in Pascal, and so was the Berkeley P-System, a portable Pascal development environment from the 1970s, featuring a virtual machine that influenced the later JVM. Apple's Lisa OS was also implemented in Pascal.

UCSD p-System perhaps?

Yes, Apple II GS had a Pascal OS fully based on it.

http://pascal.hansotten.com/ucsd-p-system/apple-pascal/apple...

Indeed, e.g. Apple Lisa OS and the first Mac OS. But the present one so far is only around 100 lines; the author calls it a "bootloader". Here is a list of more complete systems: https://wiki.freepascal.org/Operating_Systems_written_in_FPC.

My employer (France Telecom) had a Unix written in Pascal running on a 68000 machine. But there were all the usual Unix tools on it, including a C compiler.

I used Apollo Aegis (later Domain), Three Rivers PERQ and CDC NOS, all written in some variant of Pascal.