Kanboard - Kanboard is a free and open source Kanban project management software.
Xmind - Xmind is a brainstorming and mind mapping application.
Excalidraw - Excalidraw is a whiteboard tool that lets you easily sketch diagrams that have a hand-drawn feel to them.
MindMeister - Create, share and collaboratively work on mind maps with MindMeister, the leading online mind mapping software. Includes apps for iPhone, iPad and Android.
Kinopio - Thinking canvas for mind mapping, brainstorming, and moodboards
FeatureMap - FeatureMap story mapping, simple and effective realtime collaboration and collective intelligence tool.