For writing reactive programs, we need a library. There are several reactive programming libraries for Kotlin out there to help us on these. Here's a list of the available libraries:

• RxKotlin
• Reactor-Kotlin
• Redux-Kotlin
• RxKotlin/RxJava and other Reactive Java (ReactiveX) frameworks can also be used with Kotlin (as Kotlin is 100% interoperable with Java-bidirectional)

In this book, we will focus on RxKotlin.