Freemind - Freeware MindmappingFreeMind is a very good free, open source, mind-mapping software written in Java. A mind map is a diagram used to represent words, ideas, tasks or other items linked to and arranged around a central key word or idea.
Read more about mind maps i Wikipedia
Free Mind is useful as a study tool, for presentations, notetaking or brainstorming. It has a really neat and intuitive interface, that lets you easily add and expand or collapse new nodes in different styles to your mindmap. It is useful no matter if you are a novice at mindmaping, or an expert.
Freemind is written in Java, so you need to have the Java runtime installed. Installers are available for Windows, Linux and Macintosh OS X.
A sample mindmap created in Freemind