I am contributor to Ratpack, a Sinatra-like framework for the Groovy language. Ratpack is very good for fast development of very small web applications, and seems to compete for beefier frameworks on the JVM like Grails and Spring MVC. These are very successful in the world of the JVM, but we need small frameworks as well. The biggies can require a lot of work to start a project, but starting with a lightweight framework like Ratpack is just a matter of forking the template project and starting to code. There's a whole class of tiny app that becomes economically feasible to write when the startup costs are measures in minutes rather than hours or days.