Freeplane – Mind and Information Mapping and Associated Tools
http://freeplane.sourceforge.net/wiki/index.php/Main_Page

Freeplane is free and open source software to support thinking, sharing information and getting things done at work, in school and at home. The core of the software consists of functions for mind mapping, also called concept mapping or information mapping, and tools for using mapped information. Freeplane runs on any operating system on which a current version of Java is installed and from USB. This has been added to the tools section of Research Resources Subject Tracer™ Information Blog.