SimpMusic is a production-grade Kotlin Multiplatform music player for Android and desktop (JVM) that streams from YouTube Music's undocumented backend. The codebase is organized around a shared Compose Multiplatform UI module (composeApp), Android entry points (androidApp), a desktop entry point (desktopApp), and optional feature modules for Google Cast, Last.fm scrobbling, and crash reporting. A separately referenced core submodule supplies domain and media-service logic. Internally it uses MVVM with Koin dependency injection, Repository interfaces backed by Room entities and DataStore, StateFlow-based ViewModels, and a large custom Compose component library covering home feed, library management, playlist sync, fullscreen player, lyrics, equalizer, podcasts, Android home-screen widgets, and a desktop mini-player. The app is shipped as a packaged consumer application with Play Store metadata, GitHub Actions, fastlane changelogs, and build variants that swap real integrations for empty stubs in FOSS builds.