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): https://twitter.com/pikuma/status/1767613616214188179
(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.