Everybody knows Google Earth, program which allows to acquire satellites of the earth from pictures. But these functions are very non-specialized, offered pictures are not very scientific!
World Wind is a complete program edited by NASA allowing to sail in the world in 3D. Ite allows to zoom the height of a satellite to notice the corners of the earth. Program is intended for every users, even those working in science.
WorldWind uses several satellites to be able to give the most definite possible picture.