This link to The Architecture of Open Source Applications book was gathering dust somewhere in my ~/jot directory. In true free software spirit, it is released under a Creative Commons licence and the individual chapters are readable online. Each chapter about the architecture of a particular open source software project is written by the (co-)author of that respective project.
[…] In these two books, 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.