Penpot
penpot.app
Open-source design and prototyping platform for UI/UX teams — built on open web standards, no proprietary file formats or vendor lock-in.
Why it is useful
Penpot runs natively in the browser and reads/exports standard SVG, making it easy to move designs in and out without being locked into a single vendor's ecosystem. Full support for design systems, interactive prototyping, and developer handoff (CSS/code inspection) makes it a credible free replacement for paid design tools, and it's self-hostable for teams that need to keep design files on their own infrastructure.