vym - VYM (View Your Mind) is a tool to generate and manipulate maps which show your thoughts.
Stickies - Stickies is a PC utility written to replace Post-It-style notes left stuck to your monitor.
Linked Ideas - A macOS/iOS apps to treat ideas as links of concepts.
7 Sticky Notes - Welcome to the 7 Sticky Notes Website! 7 Sticky Notes is a cool 100% free desktop notes software that creates Sticky Notes directly at the Desktop of your computer to help you organizing your everyday tasks and to-do lists.
Freeplane - Freeplane is a powerful and free software for building mind maps.
Pystickynote - Stickynotes for your desktop easily from the command line.