Most Java web application frameworks use server-side session objects to store session state. Because this complicates scaling, I'm looking at frameworks that implement a shared-nothing architecture, e.g. the Play! Framework and Apache Click. What other frameworks should I add to this list?
GWT framework - you write full AJAX application, so you can store everything you need on client side and to server send only authorization tokens (which could be stored in memory singleton or in database for verification).
Any javascript solution for client side, where you can do the same. On client side you can use Spring MVC just for implementing business methods and allowing them via REST channels (JSON as data transfer protocol is the preferred option).