YaST - GTK
A GTK+ interface for the Suse's YaST setup tool. I have developed it as a Google Summer of Code project, mentored by Michael Meeks. Still improving and maintaining it, and hoping it gets to be the default YaST in Gnome and XFCE desktops for openSUSE 10.3.
Project page: http://en.opensuse.org/YaST2-GTK
Apoo interface
Apoo is a virtual machine used to introduce first year students of my college to low-level programming. While interpreting its own Assembly-like language, it shows the computer's state, like registers, memory and stack.
I have written a new interface in Python+GTK to replace the ugly and unfunctional Python/Tk one. It should start to get used in the 2006/07 school year.
Project page: http://www.ncc.up.pt/apoo/
Microracers
A 2D top-view car racing game, inspired on Micromachines. Still unmature, but should give some minutes of fun.
Project page: http://microracers.sourceforge.net/
SuperTux
Very fun SuperMario based platform game, currently distributed by several Linux distributions. Been a main developer during part of the 0.0.x versions and the all 0.1.x ones.
Project page: http://supertux.berlios.de/
Others
Jump'n Bump - Added simple (yet very fun) AI support, as well as mouse support. (project page)