Diagrams for Mac - A diagram editor for visualizing structures and processes
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.
Diagrammm - Fundamentals on data visualization
vym - VYM (View Your Mind) is a tool to generate and manipulate maps which show your thoughts.
Wireflow - Create beautiful flowcharts
Freeplane - Freeplane is a powerful and free software for building mind maps.