MIT 6.S081 – Operating System Engineering
OSTEP by Remzi and Andrea Arpaci-Dusseau is a great read for anybody interested in operating systems (<a href="https://pages.cs.wisc.edu/~remzi/OSTEP/" rel="nofollow">https://pages.cs.wisc.edu/~remzi/OSTEP/</a>). The projects in their class at the University of Wisconsin-Madison were mainly making edits to the xv6 OS.