When you think about Scala web applications you’re probably thinking Play. This framework to me is the de facto standard for building web applications in Scala. It offers a great set of features that make it really easy to build web applications.
The framework looks very similar to Rails and ASP.NET Core. I think it has the great things of both and adds more on top of that by enabling Akka actors and a functional programming style that I find more logical to use these days.