The IHMC (Institute for Human and Machine Cognition) has a concept map tool called CmapTools, which is free to donwload and use.
The IHMC CmapTools software empowers users to construct, navigate, share, and criticize knowledge models represented as Concepts Maps.
The following may be useful to know more about concept mapping.
Download.com Special Feature: Healthy Living Center
This resource center lists a number of good software tools to help you stay fit, healthy and happy. Try some of them.
Utilizing the power of technology, we’ve put together a pack of downloads to get you over the hump and on the road to healthy living. Just remember this mantra–stay fit, stay healthy, stay happy. An apple a day may keep the doctor away, but your PC works just as well.