From the README

Astryx An open source design system that's fully customizable and built for how we build now: by people and the agents working alongside them. Currently in Beta · Built on React 19+ and StyleX Docs · Storybook · Sandbox · Contributing · Discord Overview Astryx is an open source design system that grew inside Meta over the last eight years, where it became the most-used and largest design system in the company — powering 13,000+ apps and shaped by the engineers, designers, and product teams who depend on it every day. It ships 150+ accessible components, brand-level theming, dark mode, ready-to-ship templates, and a CLI as one cohesive system.