React Native is a cross-platform native mobile app development framework created by Facebook based on their React JavaScript library, mainly using JavaScript with JSX, ES6 (ECMAScript 6), and React.JS. It allows developers to build mobile apps using React Native components, which are then compiled into native apps that are almost identical to those written using native tools. The framework has several advantages, including reusable code, app stores, performance comparable to native apps, native UI components, hot reloading for immediate changes, testing with Expo, and the ability to modify published native apps separately. However, it also has some disadvantages, such as new technologies like JSX and ECMAScript, potential issues with native code, almost-perfect performance, and limitations in terms of platform-specific features. On the other hand, Kotlin Multiplatform is a relatively new alternative that allows developers to use a single codebase to develop apps for both iOS and Android, offering modular integration, ease of learning, a single codebase for business logic, native UI experience, and native performance. However, it has some limitations, such as being fresh out of beta, community support and libraries still growing, not being a closed solution, taking more development resources compared to Flutter, and requiring teams to be familiar with different tech stacks. Ultimately, the choice between React Native and Kotlin Multiplatform depends on an app's needs, prioritizing velocity, native performance, or ease of use.