I have contributed to several Open Source projects. You may contact me if you need more support regarding the pieces I modified or created; please note that I tend to contribute sporadically to most projects I'm involved in, and may have left most of them for many years now, in which case you should rather go to the current maintainer of that project.
Here's a list of projects I occasionally like to look up to see how they come along...
Five friends (Wastl, Podi, Chris, Michi and some whose name I forgot) and me developed a Java-based graphical online MUD called "Fallen Realm" (TFR, TFRlib, not related to anything you find today if you search the web for those keywords). It was first hosted on a university server, then on SourceForge, but seems to have been deleted from both of them. Today everyone knows about "MMORPGs" - TFR certainly was not massive (it did not even have one single player outside of the team...), but it was extremely interesting to program things like A* movement algorithms, server bookkeeping for lots of entities and huge maps, a tight binary client-server protocol, 2D ISO graphics algorithms and tools (that was in the days of JDK 1.2, i.e. no sophisticated 2D graphics libraries in standard Java, and we're talking 386 CPUs here!), ISO graphics rendering in POV-Ray, etc. etc. etc.. To get a glimpse at the fascination of (the theory of) game programing, see the excellent Amit's Game Programming Information.
The project ended when the team of students all got more busy; you can still look at the old TFR web site. Disregard anything about "current development" on these pages, the project is definitely not developed anymore. You can also download tfr.tar.gz here. The archive contains both the "tfrlib" and the original "tfr shard" (think "game world") with all code, graphics, and HTML documentation. Everything is under the GNU General Public License.