React Native is an open-source framework (a set of libraries and tools that gives an app its structure) for building native mobile apps with React, a JavaScript library for user interfaces. Meta released it in 2015 and has maintained it since; many companies and individual contributors now develop it, and its README points to the React Foundation.
The developer writes the interface as React components in JavaScript. React Native renders them with the platform's own interface elements: core components such as View, Text and Image map to the native building blocks of Android and iOS, so the app uses the same platform APIs as other apps. Native Modules let the JavaScript code call platform code directly. With Fast Refresh, a change to the JavaScript code appears in seconds without a rebuild of the native app. Community projects extend it to Windows, macOS and the web, and the project recommends a framework such as Expo for routing and native features.
React Native is free software under the MIT license, developed in public on GitHub.