Invision - Prototyping and collaboration for design teams
Freeplane - Freeplane is a powerful and free software for building mind maps.
Marvel - Turn sketches, mockups and designs into web, iPhone, iOS, Android and Apple Watch app prototypes.
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.
Axure RP - The prototyping and specification software used by 87% of the Fortune 100. Beyond mockups, design interactive prototypes for business solutions, websites, and applications.
vym - VYM (View Your Mind) is a tool to generate and manipulate maps which show your thoughts.