The Architecture of Open Source Applications, Volume II: Structure, Scale, and a Few More Fearless Hacks, a book edited by Amy Brown and Greg Wilson, is about the thinking and process behind many popular open source applications.  Each chapter is written by an expert of the software, for Moodle this expert is Tim Hunt (@tim_hunt) of the Open University.

According to the site,

the authors of four dozen open source applications explain how their software is structured, and why. What are each program’s major components? How do they interact? And what did their builders learn during their development? In answering these questions, the contributors to these books provide unique insights into how they think.

The PDF of the book is available for just $9.99 and all proceeds go to Amnesty International.  Click here to make a purchase (paperbacks are also available): http://www.aosabook.org/en/index.html

To read Tim’s Moodle chapter visit http://www.aosabook.org/en/moodle.html.