To make desktop application from HTML application, you'll need JS libraries that can call native OS API, something like node-ffi, node-webkit or appjs[3], that allows use native API, but they all work under node.js framework. Or you can try use browser API for access to OS functions, Firefox[4] and Chrome[5].
If you need to develop simple web application, try use HTML pages + JS + CSS + WebSQL or localStorage.
Here[6] you can learn more about HTML5.
3 - appjs.com/
4 - developer.mozilla.org/en-US/docs/Web/API/Using_the_Browser_API
5 - developer.chrome.com/extensions/api_index
6 - slides.html5rocks.com/#landing-slide