Marble is a Virtual Globe and World Atlas that you can use to learn more about Earth: You can pan and zoom around and you can look up places and roads. A mouse click on a place label will provide the respective Wikipedia article.
Marble is also a light weight generic geographical map component for use in your own Qt 4.x / C++ application. It is provided as a library, a QWidget and a KDE 4 KPart and hence can easily get integrated with KDE 4 or Qt 4 applications. By default MarbleWidget shows the earth as a sphere but doesn't make use of any hardware acceleration.