What is Spray

A framework, as we’d like to think of the term, gives you a “frame”, in which you build your application. It comes with a lot of decisions already pre-made and provides a foundation including support structures that lets you get started and deliver results quickly. In a way a framework is like a skeleton onto which you put the “flesh” of your application in order to have it come alive. As such frameworks work best if you choose them before you start application development and try to stick to the frameworks “way of doing things” as you go along.

Spray was designed specifically as “not-a-framework”, not because we don’t like frameworks, but for use cases where a framework is not the right choice. Spray is made for building integration layers based on HTTP and as such tries to “stay on the sidelines”. Therefore you normally don’t build your application “on top of” spray, but you build your application on top of whatever makes sense and use spray merely for the HTTP integration needs.

http://spray.io/introduction/what-is-spray/