Project Management Tool for Linux?

Dr. Fong asks: "We are a small start-up, and we're finding that as we grow our need for a project management tool for our development efforts is increasing. We've trawled FreshMeat and a number of other software databases and have not been able to find a tool to fit our requirements. Can anybody recommend a Project Management tool that has GANTT and PERT charts and allows you to allocate work to a number of developers? Web based visualisation/updates would be a bonus."