Taskjuggler is an interesting option for project managers using Linux. The program seems to be pretty complete with all the bells and whistles to keep track of tasks, time, resources, and costs.

From the site, here is a couple of its features:

• Automatic resource leveling, tasks conflict resolutions, and task filtering
• Comprehensive and flexible views and reports so you can find the information you need when you need it
• Built-in templates to get you started
• Unlimited number of scenarios (baselines) of the same project for what-if analysis
• CSV data export for exchange with Office Suites
• Risk analysis
• Flexible working hours and vacation handling
• Multiple time zone support
• Generation of iCal files for data exchange with standard productivity tools