Compose Multiplatform is a modern UI toolkit developed by Google that allows developers to build native UIs for Android, iOS, and the web from a single codebase. It provides a declarative and reactive approach to building user interfaces, and is designed to be fully interoperable with existing Kotlin code. Compose Multiplatform is built on top of Kotlin Multiplatform, which allows developers to share code across different platforms, and provides a range of tools and APIs for building powerful and responsive UIs. It is a powerful and flexible toolkit that can be used to build a wide range of applications, from simple mobile apps to complex web applications. Compose Multiplatform is still in development, but it is already being used by many developers and companies to build modern and efficient user interfaces for their applications.