ArcGIS Earth - Allows you to explore any part of the world. Work with a variety of 3D and 2D map data formatt, including KML. Display data, sketch placemarks, measure and perform interactive analysis, and add annotations.
Google Earth - A computer program that renders a 3D representation of Earth based on satellite imagery.
Skyline - 3D desktop and web-based applications, enabling an enterprise to build, edit, navigate, query, and analyze realistic 3D environments.
World Wind - An SDK (software development kit) that software engineers can use to build their own applications
Earth Enterprise - the open source release of Google Earth Enterprise, a geospatial application which provides the ability to build and host custom 3D globes and 2D maps.