Author here. I cover the three main implementations of Reactive Streams, RxJava, Reactor (from Spring), and Akka Streams.
The books goes into some depth, covering not only the overview of the API but what back pressure is, how to handle it, how to test Streams, and the book then implements three applications using each library.
1) An Android app with RxJava. 2) A WebFlux Spring Boot app using Reactor. 3) A web socket chat application using Akka Streams.
All of these example are available on github and in the code download associated with the book.