Books

Learning Concurrent Programming in Scala https://www.packtpub.com/application-development/learning-concurrent-programming-scala-second-edition

Applied Akka Patterns http://shop.oreilly.com/product/0636920043577.do

Reactive Extensions

http://reactivex.io

https://github.com/ReactiveX/RxScala/blob/0.x/examples/src/test/scala/examples/RxScalaDemo.scala

Concurrency inside JVM

http://tutorials.jenkov.com/java-concurrency/concurrency-models.html

https://stackoverflow.com/questions/2213340/what-is-daemon-thread-in-java

http://blog.jessitron.com/2014/01/choosing-executorservice.html

Futures

http://rerun.me/2016/06/05/scala-notes-futures-2-promises/

https://stackoverflow.com/questions/18960339/clarification-needed-about-futures-and-promises-in-scala

Akka

https://www.chrisstucchio.com/blog/2013/actors_vs_futures.html

http://pchiusano.blogspot.com.br/2010/01/actors-are-not-good-concurrency-model.html

http://www.deadcoderising.com/2015-05-26-akka-change-an-actors-behavior-using-context-become/

General

http://robotlolita.me/2015/11/15/how-do-promises-work.html