Open Source Design & Prototyping Tools

Design & Prototyping is one of the most active slices of the open source world — the 5 projects below are ranked by GitHub stars, which makes this page roughly a community-voted shortlist rather than a vendor-curated catalogue. Every card shows the license and the last-commit date, so you can filter out the two failure modes of free software in one glance: restrictive licensing that blocks your use case, and abandonment that leaves you maintaining a fork. When two projects look comparable, prefer the one with more recent activity and the more permissive license (MIT/Apache-2.0 over AGPL) unless copyleft specifically serves your goals. Hover into any project for its full README — the documentation quality is usually the honest tell of engineering quality.