Bill Atkinson's QuickDraw is one example of that. The original was written for the Lisa in Pascal, and then brought over to the Mac project. And I believe portions rewritten in assembler for compactness/speed.

The Mac version of QuickDraw is here: https://computerhistory.org/blog/macpaint-and-quickdraw-sour...

Now that both are "open", it would be interesting to compare the two and see how they differ.