The G1 runs on the Android operating system. Most Android software developers write their applications in Java, but since Android does not directly run J2ME applications, they need to be compiled first to a unique non-Java bytecode before they can be executed on an Android powered phone. The home screen app provided on the G1 offers a desktop with shortcut icons similar to the one on Windows mobile devices, but gives the user three screens worth of space for storing more shortcuts than will fit on one screen. Dragging sideways across the home screen scrolls between the desktops. The G1 comes with ChromeLite a stripped down version of the Google Chrome browser.
Other software applications can be downloaded from the Android Market, which hosts existing and new services from developers. The device comes preloaded with several Google applications like Maps (including satellite view, traffic and Google Street View with a built-in compass), GMail, a dedicated YouTube player, Calendar, and Google Talk.
GPS navigation is available through a built-in GPS receiver.Maps are displayed in a conventional 2D display or an overhead satellite view; the inbuilt digital compass also allows the navigation of street views in real time. The G1 comes with Amazon's MP3 mobile application. Users can connect to Amazon.com online digital music store to browse and purchase from available titles.
Information taken from Wikipedia.