Most AI app tools spit out code — then you're stuck wiring auth, payments, biometrics, and a UI that looks AI-made. Sigma Stack is a production-ready React Native template with the boring 80% already done: splash, onboarding, auth, biometrics, profile + edit, settings, theming, notifications & permissions, multilingual — with Supabase and RevenueCat wired in. It ships with a React Native engineer agent that builds your features on top, so you start at "build my app," not "set up my app."