Is it possible to have a mobile website that can still function if there's no internet connection?
The user should still be able to use the website (if he has visited that page before), see the data (that was loaded before), add new stuff (cache locally). When internet connection comes back online, all changed local data should be pushed online.
This should be a complete webbased solution, not a native app.
You should have a look at HTML5 offline storage, see http://diveintohtml5.ep.io/offline.html and the Offline Web Applications spec as a start. There are also quite a few posts here on SO.
Bookmarklets work when a user is offline. The trick with a bookmarklet is that it's entirely self contained javascript wrapped up in such a way that it can live within the bookmark itself. E.g. a javacsript: URL. You can also have a data: URL as a bookmark, which could be a complete HTML page. Usually these are base64 encoded with a mime type.
Probably what I'd do would be have a small base page as data:text/html,base64 which contained whatever offline content you cared about, but periodically tried to bootstrap the rest of the "real" content from wherever you host it.
