Excalidraw is a virtual collaborative whiteboard for sketching hand-drawn-like diagrams. Open source, end-to-end encrypted, and runs entirely in the browser.

A virtual collaborative whiteboard for sketching hand-drawn-like diagrams. All processing happens in the browser — no data is stored on the server.
Single container (nginx), no database. All drawing data stays in the browser. End-to-end encrypted when using live collaboration.
MIT — GitHub