Open Source project management tools [1] is a comprehensive list of PM tools available on the market... actually the longest list I have have found so far...

some notable tools on there to check out:

MySQL Eventum [2] the mySQLab Issue / Bug Tracking System with project management features based on MySQL

Trac [3] is a python based tool, also integrating into the software confguration management subversion and allows WIKI syntax throughout the whole management process...

PHProjekt [4] - this PHP based suite even features an outlook sync feature in beta!

Those tools look very close to bug tracking tools and I am keen to find out what their real "project management" capabilities really are...

Also dont forget to checkout OpenPSA [5] the OS professional services automation suite including a lot more business related functions.