The Open Source but Windows-only...

NASA World Wind 1.4

...was released on Valentine's Day. It is described as World Wind lets you zoom from satellite altitude into any place on Earth. Leveraging Landsat satellite imagery and Shuttle Radar Topography Mission data. You can also find the official support site wiki at...

World Wind Wiki

World Wind depends on both Microsoft's .NET and DirectX which explains why it has not be ported to Mac OS X or Linux.