TiddlyWiki - a non-linear personal web notebook
Xmind - Xmind is a brainstorming and mind mapping application.
wikidPad - wikidPad is an application for storing thoughts, ideas, todo lists, contacts, or anything else that user can think of to write down.
Visual Understanding Environment - Visual Understanding Environment (VUE) is a mind-mapping and concept-mapping tool.
Knowledge Workshop - Learning Management Solutions provides innovative and reliable software for the knowledge worker.
FreeMind - FreeMind is a premier free mind-mapping software written in Java.