Excalidraw is an open-source virtual whiteboard for sketching diagrams that look hand-drawn. It runs entirely in the browser with no signup required: open the canvas, draw shapes, arrows and text, and you have a quick wireframe, flowchart or napkin sketch in seconds. Drawings stay end-to-end encrypted in collaborative rooms, so two or more people can co-edit a board in real time without an account.

The project started in 2020 and is now a fixture in the developer and design community, used at companies like Meta, Microsoft and Stripe for ad-hoc whiteboarding during interviews and design reviews. The MIT-licensed editor can be embedded in any app via @excalidraw/excalidraw, and there is also a paid hosted offering, Excalidraw+, that adds shared workspaces, version history and SSO for teams who want a managed version on top of the free core.