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.
vym - VYM (View Your Mind) is a tool to generate and manipulate maps which show your thoughts.