Freeplane - Freeplane is a powerful and free software for building mind maps.
WriteNext - The writing application that boosts your writing. Increase focus and writing performance and reduce distractions by separating your creative writing from other activities. Let writing be the only activity you perform in the writing application.
vym - VYM (View Your Mind) is a tool to generate and manipulate maps which show your thoughts.
Stashany - Online notepad for developers
Pencil Project - Single-user mockup / wireframing / diagramming tool
Calmly Writer - Distraction-free text editor for Mac, Windows, Linux and ChromeOS.