HTML5 is just one of the essential features for HTML based phone apps that provide the scaffolding. You will also need CSS3 to dress it up in more delightful ways and of course JavaScript to power the interactivity of the app without which it is dead in the water. While you could use DOM and vanilla JavaScript, it is lot more easier to use a framework (there is a learning curve), a User Interface Framework which combines JavaScript with CSS to provide a set of programming tools to deliver rich mobile applications. Quite a lot of them use jQuery in one form or another. The frameworks save a lot of development time and effort. There are different kind of devices (iPhones, Androids and Windows Phones) but also different operating systems (iOS, Android, Windows Phone, etc) and it will be desirable if one could use one tool to cover all these variations. This area has developed to the extent that you can develop cross-platform, cross-device (response design!) apps but still there iss...