VisualSitemaps - Autogenerate visual sitemaps in seconds.
vym - VYM (View Your Mind) is a tool to generate and manipulate maps which show your thoughts.
Codrops Blueprints - Free website concepts ready to implement or modify
Linked Ideas - A macOS/iOS apps to treat ideas as links of concepts.
Octopus.do - Build your website structure in real-time and rapidly share it to collaborate with your team or clients. Start prototyping websites or apps instantly.
Freeplane - Freeplane is a powerful and free software for building mind maps.