Free Mindmapping Tools

Mind mapping software is used to create diagrams of relationships between ideas or other pieces of information. A concept map is a special form of a web diagram for exploring knowledge and gathering and sharing information

Concept and Mind Mapping Software

CMapsTools http://cmap.ihmc.us/  IHMC CmapTools program empowers users to construct, navigate, share and criticize knowledge models represented as concept maps

VUE http://vue.tufts.edu/ is a concept mapping tool to organize, visualize, and present ideas.

XMIND  http://www.xmind.net/   .  XMind is a concept mapping tool, and a mind mapping tool,

Mind Mapping FreeMind is a mind mapping application written in Java
http://freemind.sourceforge.net/wiki/index.php/Main_Page