Kotlin is the language Google now recommends for Android, so it's no surprise the free course here comes from Google itself. Android Basics with Compose is a real commitment at around eighty hours, and it teaches Kotlin and the modern Compose UI toolkit together, so you finish with working screens on a phone instead of console output. It's interactive and codelab-guided, and it assumes no prior Kotlin. Be straight with yourself about the shape of this catalog before you start: Kotlin's free course space is thin compared to Python or JavaScript, and this is the one course worth your time. If you already program in another language and want the syntax on its own first, JetBrains' free Kotlin Koans exercises at play.kotlinlang.org fill that gap in an afternoon. And if you want Kotlin for backend (Ktor) or multiplatform work rather than Android, you'll outgrow anything here quickly and move on to the official docs and your own projects.
Google's official Android development course teaching Kotlin and Jetpack Compose. Build real Android apps from scratch: UI, state, navigation, data persistence, and networking. Free, with hands-on codelabs at every step.