Ask HN: What source code is worth studying?  
There is a good book on this theme
<a href="http://aosabook.org/en/index.html" rel="nofollow">http://aosabook.org/en/index.html</a><p>, where the authors actually go deep into the design & architecture of selected <i>well designed</i> open source projects
e.g. llvm, git, freeswitch, etc.<p>Highly recommended !