Akka in Action.
This is an excellent book by Raymond Roestenburg, Rob Bakker, and Rob Williams. Whilst the hardbook isn’t out until December, all chapters are now available as an eBook under Manning’s Early Access Program.
Akka in Action uses examples (in Scala) on how you can build message-oriented systems using Akka. The book also includes sections on patterns like Event Sourcing, and CQRS.
On the Kindle version, the code isn’t formatted as well as it should be so you’ll find yourself switching back and forth the code cloned from the associated GitHub repo.
All in all, an excellent addition to any software engineer using Akka.