Freeplane - Freeplane is a powerful and free software for building mind maps.
Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
Linked Ideas - A macOS/iOS apps to treat ideas as links of concepts.
Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.
vym - VYM (View Your Mind) is a tool to generate and manipulate maps which show your thoughts.
Slack - A messaging app for teams who see through the Earth!