Prototyping Tools - Find the Prototyping Tool You Need
Linked Ideas - A macOS/iOS apps to treat ideas as links of concepts.
iOS Design Kit - The newest library of native iOS templates
Freeplane - Freeplane is a powerful and free software for building mind maps.
Pencil Project - Single-user mockup / wireframing / diagramming tool
vym - VYM (View Your Mind) is a tool to generate and manipulate maps which show your thoughts.