GanttProject is a cross-platform desktop tool for project scheduling and management. It runs on Windows, Linux and MacOSX, it is free and its code is opensource. What can it do?

Gantt chart: create work breakdown structure, draw dependencies, define milestones.
Resources: assign human resources to work on tasks, see their allocation on the Resource Load chart.
PERT chart: generate PERT chart from Gantt chart.
Export: save charts as PNG images, generate PDF and HTML reports.
Interoperate; import projects from and export them to Microsoft Project formats. Export to spreadsheets with CSV.
Collaborate: share projects with your colleagues using WebDAV.