In this case, my favorite back-end language is Scala, with the Play Framework. It has an excellent threading model, asynchronous processing, stateless model, a

In this case, my favorite back-end language is Scala, with the Play Framework. It has an excellent threading model, asynchronous processing, stateless model, a functional, immutable data programming style that fits well with multi-threading, great performance, and access to a vast array of Java libraries and tooling.