Freeplane - Freeplane is a powerful and free software for building mind maps.
Novelize - Novelize is an online novel writing app designed to keep authors on track.
Linked Ideas - A macOS/iOS apps to treat ideas as links of concepts.
Manuskript - Open-source tool for writers.
vym - VYM (View Your Mind) is a tool to generate and manipulate maps which show your thoughts.
BlankPage - Stay motivated to write, and finish your story