The Play framework
The Play framework is a web framework built on top of Akka. It has a proven track record in industry, and is thus a reliable choice for building scalable web applications.
Play is an opinionated web framework: it expects you to follow the MVC architecture, and it has a strong opinion about the tools you should be using. It comes bundled with its own JSON and XML parsers, with its own tools for accessing external APIs, and with recommendations for how to access databases.