Path breaking and, probably, the most exciting feature in Kotlin are coroutines. They are a new way to write asynchronous, non-blocking code somewhere like the threads, but way more simple, efficient, and lightweight. Coroutines were added in Kotlin 1.1 and are still experimental, so think before using it in production.
In the later chapters of this book, you'll learn about Schedulers in RxKotlin, which encapsulates the complexities of threading, but you can use it only in RxKotlin chain, while you can use coroutines anywhere and everywhere. That is indeed a path-breaking feature of Kotlin. They provide a great abstraction on threads, making context changes and concurrency easier.
Keep in mind that RxKotlin does not use coroutines ...
