This course introduces the concepts and frameworks used to develop applications that run seamlessly across multiple operating systems, such as Android, iOS, and the web. The curriculum focuses on "write once, run anywhere" strategies using modern tools like Flutter, React Native, or Kotlin Multiplatform. Students explore cross-platform UI components, state management, and API integration. The course emphasizes the trade-offs between native and cross-platform development regarding performance and user experience. By the end of the semester, students will be capable of building and deploying functional, responsive applications from a single codebase for various digital environments.