If you're an advocate for open-source software and prioritize privacy, Penpot is your best choice. It's designed for teams that value collaboration and offers a solid framework for prototyping within an open standards ecosystem. However, if your workflow relies on a robust plugin ecosystem and highly polished features, Penpot may fall short due to its smaller community and performance compared to tools like Figma.
On the other hand, if you seek a charming, low-fidelity approach for brainstorming or sketching out ideas, Excalidraw is perfect. Its hand-drawn aesthetic makes it ideal for developers looking to visualize architecture quickly or teams needing a free-form space for brainstorming. However, if you require a full-fledged design tool capable of producing high-quality visuals, Excalidraw's limited feature set means you'll have to look elsewhere. Choose based on your specific needs: collaboration and design fidelity with Penpot, or sketching and quick ideation with Excalidraw.