Refactotum is a weekly series that teaches, by example, how to refactor code and contribute to open source projects. Here's how it works: We pick a project, download the code, and run the test suite. We then find code to refactor, testing all the way and taking notes. At the end, we convert the notes into essays or presentations, and contribute the code back to the community.
Each Refactotum project is time-boxed to four hours of dev effort. That's not much time; you can do it too.
Past refactorings include: