[muzani]

Operating Systems back in uni (UNSW). Hack your own mutex in two weeks, then hack virtual memory in two weeks, then hack a file system in two weeks. Of course we have other classes with their own assignments too, so you'd have to get all this done within a day.

What's great about it vs other courses is you had to understand an extremely complex thing and learn to modify it, instead of building something from scratch. In the real world, many things are not documented or misdocumented, so it's a vital skill to be able to understand how something works from the code.