React Native is a framework derived from React that allow to program mobile native apps using Javascript. It’s only focused on Android and iOS, but its popularity has lead to other implementations of its API for other platforms like Windows, macOS or also web. Thing is, although they share the same APIs and source code is (almost) compatible between them, they are not integrated so it would surface difficulties to add a new platform to an existing code, or forcing to have several different projects that could lead to duplicated efforts or diverge the features of them.