Visual Understanding Environment - Visual Understanding Environment (VUE) is a mind-mapping and concept-mapping tool.
Xmind - Xmind is a brainstorming and mind mapping application.
Flying Logic - Highly visual software for planning support used by strategists, process improvement specialists, teachers, and writers. Windows, Mac OS X, and Linux.
FreeMind - FreeMind is a premier free mind-mapping software written in Java.
yEd - yEd is a free desktop application to quickly create, import, edit, and automatically arrange diagrams. It runs on Windows, Mac OS X, and Unix/Linux.
PMM - Personal Memory Manager - Personal Memory Manager helps you spin-off from the top: manage your own knowledge and ideas.