If you just want basic Gantt charts there are a few like ...

planner ( http://live.gnome.org/Planner ) - seems to have stalled
GanttProject ( http://ganttproject.biz/ )

... not listed there.

But that wiki page looks good to start.

I looked for ages for something with more than just gantt charts including proper time tracking. I never found anything suitable (that was free/open source). I got somewhat forced out of that position so it's not my problem anymore. We now use nothing which works extremely well </sarcasm>

Good luck