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

Workflowy - A better way to organize your mind.

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

Checkvist - A professional list-making tool. Minimalist, keyboard-centric online outliner and task management application. Free sharing, unlimited lists, cross-linking, free import and export. Markdown support. Created for geeks 🤓 and all keyboard lovers ⌨️

Linked Ideas - A macOS/iOS apps to treat ideas as links of concepts.

OmniOutliner - OmniOutliner is a writing app for collecting information, outlining ideas, adding structure to any sort of writing.