For product teams and developers focused on building custom canvas applications, tldraw is your best pick. Its polished infinite canvas and real-time collaboration features make it ideal for creating working user interfaces directly from sketches. However, if your needs involve commercial use, be prepared to pay for a license to remove watermarks.
On the other hand, if you're a developer or designer needing a low-stakes tool for quick brainstorming sessions, Excalidraw's open-source, hand-drawn aesthetic offers a charming and informal environment. It’s perfect for capturing quick ideas or architectural sketches but falls short for those requiring high-fidelity polished diagrams or a full design tool. Choose Excalidraw for casual use, but avoid it if you intend to create more refined visuals.