Astryx

Astryx is a fully customizable, open-source design system built by Meta, powering over 13,000 internal apps. Engineered for both human developers and AI coding agents, it features 150+ accessible React components styled with StyleX (with no build plugins required). What sets it apart is its open-internals architecture—allowing you to swizzle and extract full component source code—and strict API predictability that ensures LLMs and humans can build seamlessly together.