Freeplane - Freeplane is a powerful and free software for building mind maps.

Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.

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.

Google Docs - Create a new document and edit with others at the same time -- from your computer, phone or tablet. Get stuff done with or without an internet connection. Use Docs to edit Word files. Free from Google.

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

Nuclino - Nuclino works like a collective brain, helping teams bring all their knowledge, docs, and projects together in one place. It's a modern, simple, and blazingly fast way to collaborate.