If you're interested in learning operating systems or compilers the TempleOS source is surprisingly approachable and clocks in at around 100K LOC. I did a deep

If you're interested in learning operating systems or compilers the TempleOS source is surprisingly approachable and clocks in at around 100K LOC. I did a deep dive of HolyC while on a long bus drive and came away with a lot. Terry Davis often talked about the importance of simplicity (albeit using more colorful language) and you can see that throughout his work.