Aladin is an interactive sky atlas allowing the user to visualize digitized astronomical images or full surveys, superimpose entries from astronomical catalogues or databases, and interactively access related data and information from the Simbad database, the VizieR service and other archives for all known astronomical objects in the field. It is a free and open source astronomy analyzing application that's comprehensive, reliable and advanced.
Here are some screenshots to illustrate the features and user interface of this application:
OkMap
Quantum GIS
Stellarium
Garmin Express
Hallo Northern Sky