KotlinKoans
You can play with Koans online: https://play.kotlinlang.org/koans/overview.
You can solve the tasks right inside IntelliJ IDEA or Android Studio by installing the EduTools plugin and choosing Kotlin Koans course.
Introduction
Here you can find all the challenges done and ready together with the explanation of each task and example.
Tools used
Go ahead and use the latest IntelliJ it have the setup for the project to run single examples
Licenze - MIT
Feel free to use. If you can add me to any credits would appreciate it. Thanks.