Projects I’m involved in:

• PyInstaller: a multi-platform Python packager. Similar to py2exe and py2app, but fully multi-platform, and with many advanced features, like builtin support for many 3rd-parties libraries.
• BeRTOS: a free real-time operating system released by Develer. I mainly follow its development (well run by my colleagues) and help out with ideas and reviews. I have lately contributed a (not yet complete) cryptographic library.
• TomatoUSB: a very advanced distribution for Broadcom-based routers, based on the famous Tomato, but with full USB support. My involvement is mainly small bugfixes, documentation and tutorials (I basically use it at home and contribute back in terms of writing down what I do). I am also the administrator of the website, which I have contributed to the project. I’m working on a large patch to give it a plugin-based support for extensions, but it’s probably too large to be ever finished (by me at least).

Projects I have contributed to:

• GCC: I used to contribute to the C++ frontend, specifically for improving template compatibility and error detection. I have also contributed a large refactoring to shrink a very commonly used internal data structure, for memory efficiency. Though I am still listed among the official maintainers, I just silently follow its development now.
• svnmerge: the de-facto standard for Subversion merge tracking, until Subversion 1.5 was released. I joined the project at the very beginning, when it was still a bash script, and converted it to Python to ease maintenance. I added a testsuite and many features. Later, when several good developers joined in, I served as maintainer and code reviewer.
• SIP: A Python binding generator for C++ code. Similar to SWIG and Boost.Python. It is maintained by Riverbank Computing as the tool to generate PyQt. I have submitted some patches and help some fellow Develerians develop others.

Then, there would be a long list of projects to which I have just contributed a single patch, without ever getting involved in real development.  But would anyone be interested in such a list? In fact, Google can probably populate it better than my memory.