Excalidraw

Excalidraw is an open-source virtual whiteboard for sketching diagrams with a hand-drawn look, used directly in the browser with no account needed. Drawings save to the browser by default and can be exported or shared, live collaboration runs through end-to-end encrypted links, and keyboard shortcuts cover every tool. Its welcome screen is hand-lettered in the same style as the drawings, with arrows pointing out the toolbar and menus.