Project management tools
Free
In this 2016 article at Opensource.com the top 11 project management tools for 2016 that are Free / Libre Open Source Software (FLOSS) [1], they list
- MyCollab AGPLv3, Java, MySQL
- Odoo GPLv3, limited feature community edition
- Taiga GNU Affero GPLv3, stack includes Nginx, Python and PostgreSQL You can start a project at taiga.io
- OrangeScrum GPLv3, based on CakePHP
- Tuleap GPLv2 - a large complete system
- Agilefant (license)
- Redmine GPLv2 RoR
- [Project-open] (dual license)
- OpenProject GPLv3
- LibrePlan GPLv3 Java, PostGreSQL, Tomcat
- ProjectLibre Common Public Attribution License v1 Java
I personally have used and would recommend TaskJuggler and FreeMind as well as simply organizing content and project documentation in a wiki.
Non-free
If you use Google Apps, or if you just want a quick online tool, you might want to check out http://gantter.com/gantter-editions/
Interesting and easy to use is Kanboard MIT license