G.ho.st is an excellent Os showing the capability of cloud. Already you can do many things using it like using torrent , watching movies, browsing net (though that feature is still in its alpha stage). Also you can play some flash games. Also there is a feature called G.ho.st Sync which sync the local files and remote files. You can also backup files and shared them publicly.
You can use google apps like gmail, google docs e.t.c. Also there are many apps made by users and shared but it must be also noted that many of them were same. They were earlier called g.ho.st but now they have changed it to ghost.cc( Global hosted operating system cloud computing). Earlier it was just available as desktop but now they are available as portal also.
It is still in beta stage. They are using amazon services.
PS: Any one using trying to use it can give my referral lukeskywalker