This is a project-oriented course working directly with the Mozilla (Firefox/Thunderbird) and OpenOffice.org communities. Each of these communities maintains a huge codebase (millions of lines of code) which has been developed over a number of years and which is being actively improved by hundreds of contributors from many different countries. This software is written in several languages, including C/C++, JavaScript, Java, and various scripting languages (bash, perl, and python). The software is cross-platform and works on a wide range of platforms including Windows, Mac, and Linux systems.