Kanboard - Kanboard is a free and open source Kanban project management software.
Sketchboard.io - Visual Remote Teamwork. Solve problems and create ideas on endless whiteboard with your teammates by sketching.
Kinopio - Thinking canvas for mind mapping, brainstorming, and moodboards
Draw.Chat - Anonymous real-time whiteboard with text and video chat.
Excalidraw - Excalidraw is a whiteboard tool that lets you easily sketch diagrams that have a hand-drawn feel to them.
Bluescape - Bluescape is a visual collaborative workspace designed to elevate work that empowers creation, collaborate, and innovate across the entire enterprise.