Freeplane - Freeplane is a powerful and free software for building mind maps.
Witeboard - A real-time whiteboard for your team. No signups required.
vym - VYM (View Your Mind) is a tool to generate and manipulate maps which show your thoughts.
Whiteboard Fox - Simple Online Whiteboard
SuperNotecard - Introducing SuperNotecard. SuperNotecard is an online writing tool that features virtual notecards to help arrange facts or scenes, track details, organize paragraphs, and clarify your composition process.
Mural - MURAL is a visual collaboration workspace for modern teams.