If you're a developer sketching architecture or need to brainstorm quickly, Excalidraw is the right choice. Its charming hand-drawn aesthetic lends itself well to informal sketches, and it offers the benefit of local data storage and offline functionality. However, if you require high-fidelity, polished visuals or a comprehensive design tool, Excalidraw will fall short.
On the other hand, if you need an open-source design and prototyping tool that supports real-time collaboration and is built on SVG standards, go for Penpot. It's ideal for privacy-conscious teams and open-source advocates, but be aware that its ecosystem is smaller than Figma's, and the overall polish may not match that of more established tools. Avoid Penpot if you need extensive plugins and high polish in your designs.