Not really. Its for wrapping Web apps in a container for a specific platform (in other words running "natively" outside of a browser -- technically, it's a customized browser wrapper around resources that are compiled into your code, not downloaded --- at least if you want to pass iOS certification).
That being said, the HTML application cache allows you to download a web app and store it for offline use. (http://www.html5rocks.com/en/tutorials/appcache/beginner/). You can hit a URL that uses the app cache, download the code, and then go into airplane mode and hit the same URL. The app will still work. (Obviously all data must be cached locally as well, since Web Services aren't available in airplane mode.)