This is not the end. It is not even the beginning of the end. But it is, perhaps, the end of the beginning.
Winston Churchill
If you have made it this far through Hands-on Scala, you should by now be comfortable using the Scala programming language in a wide range of scenarios. You've implemented algorithms, API clients, web servers, file synchronizers, and programming languages. You've dealt with concurrency and parallelism. You've worked with the filesystem, databases, data serialization, and many other cross-cutting concerns that you would find in any real-world software system.
This book only walks you through a narrow slice of the Scala ecosystem: there is a wealth of libraries and frameworks that people use writing Scala in production, and it is impossible to cover them all in one book. Nevertheless, the core concepts you learned here apply regardless of which specific toolset you end up using. Breadth-first search is breadth-first search, and a HTTP request is a HTTP request, regardless of how the exact method calls are spelled.
Scala is a flexible, broadly useful programming language. By now you have seen how Scala can be used to tackle even difficult, complex problems in an elegant and straightforward manner. While this book is not the final word in learning Scala, it should be enough for you to take off on your own, and get started solving real problems and delivering real value using the Scala language.