Excalidraw

Virtual whiteboard for sketching hand-drawn diagrams: collaborative, encrypted, and open-source.

Excalidraw is the premier open-source, canvas-based whiteboard tool, built for rapid visual thinking. The platform delivers a distinctive, hand-drawn aesthetic while supporting essential features: real-time collaboration, end-to-end encryption, and local-first storage. Users leverage a wide range of tools (rectangle, arrow, free-draw) on an infinite canvas, exporting final work to formats like PNG, SVG, or the editable `.excalidraw` JSON file. Major organizations, including Google Cloud and Meta, utilize the editor for everything from system architecture diagrams to quick wireframing.

https://excalidraw.com