Inkscape - Inkscape is a free, open source professional vector graphics editor for Windows, Mac OS X and Linux.
Freeplane - Freeplane is a powerful and free software for building mind maps.
Sketch - Professional digital design for Mac.
Linked Ideas - A macOS/iOS apps to treat ideas as links of concepts.
Affinity Designer - Professional creative software, exclusively for Mac.
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.