Excalidraw is a simple drawing tool that produces diagrams with a sketchy, hand-drawn feel. You can create flowcharts, architecture diagrams, wireframes, and mind maps without wrestling with a complex interface. It runs in the browser, works offline, and stores files locally by default. Collaboration is supported through shareable links, and the whole thing is open source.

The hand-drawn aesthetic makes diagrams feel less formal, which is useful for brainstorming and early-stage discussions. It is not meant for polished presentations, but for getting ideas out of your head quickly. Developers often use it to sketch system designs, and product teams use it for user flows. There is also a library of reusable shapes and a VS Code extension.