I'm using it because due to performance and maturity requirements I decided to build my app on the JVM. Among the JVM frameworks I selected Play for its features (development workflow, statelessness, async, REST/JSON). Given the choice of Java or Scala, I selected Scala because it is more expressive (less, clearer code) and the functional style makes it easier to work in asynchronous and immutable style. Also, I wanted strong typing and didn't want to use Groovy or Clojure.