I have been using this application FreeMind since Uni and it has serve me well. It’s good where you would want to brainstorm some ideas plus doing other things such as ploting a tree, category, hierarchy or organizational structure. I consider it as one of the productive toolset that can be used daily.
The possibilities are endless and people are using it in different areas such as:
– Keeping track of projects
– Keeping a collection of small or middle sized notes with links on some area which expands as needed.
– Keeping a small database of something with structure that is either very dynamic or not known in advance.
– Essay writing, presentation and brainstorming
– Fold and Unfolding your ideas plus embedded and clickable links
MindManager seems to be the commercial choice for this kind of application but FreeMind is written in Java and is available for free! Open source rocks!