GMDesk is a browser-like platform dedicated to Google users. The application provides hotkey-triggered access to some of Google's services: Mail, Calendar, Docs, Maps, Reader, and Picasa Web Albums. The purpose of this tool is to save the desktop space otherwise used for opening each service individually. GMDesk is built using Adobe AIR which makes it available for Windows, Linux along with Mac systems.
Even though GMDesk is not a browser, it certainly behaves like one; you can open links outside of the Google domain (automatically in a new window) but with no address bar available. In order to keep you focused on just one task at a time, GMDesk provides a fullscreen mode for all Google services.
As a Google user myself, I can't see a valid reason for using GMDesk. It does nothing special that a modern browser can't do. With a browser you can open multiple links (in this case Google services) at the same time in different tabs. GMDesk allows users to select a startup service. With a browser, you can do the same by assigning a home page. If you are a fan of the Adobe AIR architecture in particular, then GMDesk may be worth a try.