Jolicloud is an interesting experiment that puts an HTML 5-based interface and cloud-based experience on Ubuntu Linux. Only a few apps are included with the initial installation -- not even OpenOffice! Another 650 are available to be installed as downloads from Joli's headquarters through the "My Jolicloud" App Directory application.
Some are Linux versions of popular applications, like VLC media player and OpenOffice Writer. Most are Web apps that run full-screen (in the Chromium browser, it turns out) so that they look like regular software programs. GMail is the #1 most popular "application" that you can install.
(It is a puzzle to me why I would want to "install" GMail, since I can access it through the included FireFox or Chromium Web browsers. I installed the GMail app and, sure enough, it's just regular GMail running full screen in Chromium.)
Uninstalling apps is a pain, since that has to be done by searching "My Jolicloud" for the name of the application -- no simple right-clicking of the icon, or Add/Remove mini-app. Jolicloud makes it Facebook-tough to get rid of unwanted applications.
Overall, the experience is schizoid. Parts of the OS are rendered as lovely full-screen Web pages, while other parts are still the now-familiar Linux UI, which look chunky in comparison.
I recommend you try Jolicloud if you are interested in seeing what cloud-based computing feels like. It's not Utopia; the OS's Twitter-like status messages ("ralphg installed Tweetmix. ralphg uninstalled Tweetmix") make it feel like 1984.
(You can run Jolicloud as a dual-boot OS with Windows, or do as I do: use a spare netbook computer as an OS testbed.)