ganttproject.biz offers the only free gantt chart software that I’ve come across where bars correspond to changes in dates.
It’s java based, so works on most platforms, including Mac and PC
Downbload it here www.ganttproject.biz/
There’s a tutorial to assist too:
Other alternatives can be found at:
- ganttproject.biz
- tomsplanner.com
- itaskx.com (for mac)
But I recommend GanttProject!