I've been using eGroupWare, phprojekt and dotProject. eGroupWare has nice features and modules available. We needed to make some mods to it which is not so easy due to its architecture, so we switched to dotProject. dotProject is pretty straightforward and the easiest interface, but it's lacking updates and security, so we had to modify it a bit. As for phprojekt, it's one of the oldest PHP project management tools, but its set of features seems quite limited to me.

As for Extreme Project Management which is getting more popular these days, there are just a few tools available. If you're running a software project and need some minimalistic management tool, Trac is the best to choose. For more complicated XPMT or PPTS would be better. Also take a look at XPlanner.