Stickies - Stickies is a PC utility written to replace Post-It-style notes left stuck to your monitor.
Freeplane - Freeplane is a powerful and free software for building mind maps.
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.
Linked Ideas - A macOS/iOS apps to treat ideas as links of concepts.
Pystickynote - Stickynotes for your desktop easily from the command line.
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.