While not free, Paul M Jones book Modernizing Legacy Applications in PHP has really helped me get control of a large old codebase. https://leanpub.com/mlaphp h

While not free, Paul M Jones book Modernizing Legacy Applications in PHP has really helped me get control of a large old codebase. https://leanpub.com/mlaphp https://leanpub.com/mlaphp It gives examples and goes bit by bit through the process of organizing code. I'm using its suggestions along with a static checker called Phan, which I chose because it attempts to "prove incorrectness rather than correctness." https://github.com/phan/phan https://github.com/phan/phan