We are huge fans of Pascal (and Turbo Pascal specifically) here on this site.
And today we found out that people used to write operating systems in Pascal. One such example is the classic Mac OS (not the modern macOS): pikuma.com on X: "Historically, #C was not always the default language for writing operating systems. There is a rich tradition of operating systems written in #Pascal, with the probably best-known example being classical Mac OS (not to be confused with macOS, that is written in Objective C). Up https://t.co/WDu6r3hwO6" / X
(source)
And then there is ToroOS - an operating system written in Pascal.
Another discovery - pikuma.com has great classes and is a wonderful learning resource.