This document discusses building mobile apps using HTML5, CSS3, and JavaScript. It presents three types of mobile apps: web apps, hybrid apps, and native apps. It then demonstrates building each type of app through examples on the Nokia N900: 1) a HTML5 web app using video, canvas, and other features, 2) a hybrid app with CSS3 styles and animations built using QtWebKit, and 3) a native app using JavaScript and QML to create interfaces and bind to native device APIs. The document encourages developers to start building on the N900 immediately using these techniques and tools.