GanttProject
GanttProject is free for any purposes, including commercial use. No license fees.
http://www.ganttproject.biz/
GanttProject
https://en.wikipedia.org/wiki/GanttProject
Introduction into GanttProject 2.5
https://www.youtube.com/watch?v=5rHCSa5ad34
GanttProject Development Blog
http://ganttproject.blogspot.co.uk/
Others
Project Libre – windows based
http://www.projectlibre.org/
LibrePlan – web based
http://www.libreplan.com/services-pricing/customization-development/
Libre Office
https://www.libreoffice.org/
Five free Microsoft Project alternatives
http://www.techrepublic.com/blog/five-apps/five-free-microsoft-project-alternatives/