This document discusses single-page internet applications (SPI apps) and their implementation using Grails. SPI apps use JavaScript for their model, views, and controllers in the browser, communicating with a REST API on the server. While SPI apps provide faster loading and a better user experience, they require replicating the MVC pattern in JavaScript. Grails 3.0 will support different profiles including REST that simplify the server-side logic. Popular JavaScript frameworks like AngularJS and Ember.js provide similar features to Grails like models, views/templates, and controllers. The TodoMVC site demonstrates these frameworks.