QTViewer is described as 'Libmini is free software that displays geographic terrain data at real-time. This is an example application of integrating libmini in the Qt user interface. The application, the libMini QTViewer, primarily uses libmini viewer functions but provides additional camera control'. There are three alternatives to QTViewer for a variety of platforms, including Linux, Mac, Windows, Online / Web-based and PortableApps.com. The best alternative is Google Earth. It's not free, so if you're looking for a free alternative, you could try Marble or NASA World Wind.
Google Earth lets you fly anywhere on Earth to view satellite imagery, maps, terrain, 3D buildings, from galaxies in outer space to the canyons of the ocean. You can explore rich geographical content, save your toured places, and share with others.
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.
World Wind lets you zoom from satellite altitude into any place on Earth. Leveraging Landsat satellite imagery and Shuttle Radar Topography Mission data, World Wind lets you experience Earth terrain in visually rich 3D, just as if you were really there.