Top tools: SimpleMind Pro
They say a picture is worth a thousand words. But how about a picture made up of words? Mindmaps are effective tools for organizing ideas. Using them can give your thinking structure while simultaneously allowing you maximum freedom to explore new conceptual avenues. The SimpleMind Pro application is the best we've come across, and we like their pricing structure: no subscription, just a very reasonably priced one-time purchase starting at €24.99 (about $30). It's available for macOS/Windows/iOS/Android, and they also have multi-user packages. Read this short LinkedIn article for an excellent summary of how SimpleMind can support your creative process.