GanttProject is a project scheduling application written in Java and featuring gantt chart, resource management, calendaring, import/export (MS Project, HTML, PDF, spreadsheets). Learn more on http://ganttproject.biz
not relevant for big projects (no overview before printing : JRE out of memory, zoom out limited to ~1.5year) no printing zoom. don't import MS project 2007 files
Nice to have an OS alternative to commercial software, but printing really sucks. You cannot make very complex things too. It needs work but it is open! Enjoy!