Kanboard - Kanboard is a free and open source Kanban project management software.
Taiga - Project management platform for agile developers & designers
Excalidraw - Excalidraw is a whiteboard tool that lets you easily sketch diagrams that have a hand-drawn feel to them.
Plan.io - Planio makes web based project management and team collaboration more efficient and fun. It is the perfect platform for your projects, team members and clients.
Kinopio - Thinking canvas for mind mapping, brainstorming, and moodboards
TargetProcess - Agile Project Management Web Application