Some people may ask, How can?
With Adobe Air, some developers (probably individuals) make web applications that can run on desktop, but still requires an internet connection. It also does not require an internet browser like Internet Explorer, Mozilla Firefox, Google Chrome, and the like. Many applications offered for free too.
What is Adobe Air?
Above is GeeMail screenshot, that is Adobe Air application developed from Google web mail GMail (Google Mail). To be able run GeeMail and other applications, you need to install Adobe Air on the computer first.
Interested to trying GeeMail?