These are some projects I am involved in. This is only the projects I am or was an active member of. It does not include a ton of projects I have contributed to.
GNU Emacs
I've been using GNU Emacs for a couple of years, back around 2000. But I never dived into it, and then switched to vim. But recently, I started using it again, and I liked it a lot. So much that in the first year using it, I've started contributing to it, writing patches in various area of its code base, and joining sub-projects.
Org-mode
I developed actively some parts of Org-mode, the organization mode for Emacs. My work was focused mainly on the agenda and contacts management.
el-get
el-get allows you to install and manage elisp code for Emacs. It supports lots of differents types of sources and is able to install them, update them and remove them.
I've joined my friend Dimitri on this project and helps him to make it better!
Gnus
In February 2010, I've started to use Gnus to read my e-mails in Emacs. I started hacking it on various area, and then joined the project.
Freedesktop
In June 2008, while developing awesome, I've started to contribute to various projects on Freedesktop. Some components used in awesome had to be improved, so I joined some developement team like the XCB one. I've also worked on startup-notification port to XCB.
XCB
The X protocol C-language Binding (XCB) is a replacement for Xlib featuring a small footprint, latency hiding, direct access to the protocol, improved threading support, and extensibility.
I contributed to it while developing awesome, because the version 3 is entirely based on XCB, and dropped Xlib support. At that time, awesome was one of the first project to use XCB, so we had to fix some issues in it, and improve the helper libraries.
awesome
In August 2007, I've started to work on awesome, a window manager. It's basically a frame-work where you can use and create your own UI paradigm. The default UI implementation comes with windows tiling support, message notification, various widgets, and many more things.
Debian
Since April 2002, I am an official Debian developer, and I maintain several packages.
Between 2003 and 2008, I've worked on apt-build, a tool to rebuild Debian packages the way you want (GCC flags and optimizations choice, configure options, etc).
I am also a former member of the Xen maintainers team which I started around 2006. I also did some quality assurance (QA) work (rebuilding the full archive is an example with rebuildd) and also participated in bug squashing parties. In 2006, I also worked as a Stable Release Manager.
Since 2011, I'm a co-founder and active member of the OpenStack packagers team.
Ornix
Ornix is a LUG which I created in October 2001. It's a non-profit organization which regroups free software users from Orne.
TuxFamily.org
TuxFamily is a non-profit organization aiming to provide hosting services for free software projects. After working as a system administrator for 2 years (2002-2004) for TuxFamily, I became the president of the TuxFamily.org organization in April 2004, and then retired in October 2004.
In March 2005, I came back and acted again as a system administrator, and then as a member of the administration committee in 2006.
I quited the organization definitively in November 2006.
VHFFS
VHFFS is a massive hosting platform. I've contributed to the development of the version 1, 2 and 4.
Kernel Newbies
Kernelnewbies is a website aiming to give help to people who wants to develop some things for the Linux kernel. I tried to help restoring the old Web site of kernelnewbies.org some years ago.
Linux En Rezo / SANS-Linux
Linux En Rezo (literally "Linux on network") was a french website aiming to give help to people who wanted to set up their own home-network. I wrote a lot of documentation about installing services like DHCP, Samba, BIND, Apache, etc... from 1999 to 2002. In 2001, Linux En Rezo became SANS-Linux (System Administration and Network Security for Linux), but the project finally died because I was no more able to continue, due to my work for Debian and TuxFamily.
It seems that some documentations are still mirrored.