I'm working on graph clustering and on graph visualization. My latest work is available here.
I've contributed some code to the GSL (Gnu Scientific Library). My work focused on multivariate optimization.
I used to work on Stratagus (the original name freecraft was changed after a request from Blizzard), an open source real time strategy game engine, based on ideas from Warcraft II. You can have some details here. I basically worked on the sound engine and on pathfinding (A*, see also next entry).
As a companion to two didactic articles (in french), I've written a small Java application that demonstrate different path finding algorithm implementations for tile based terrains. The source code is available (under the GPL).