From Microsoft Research:
WorldWide Telescope began in 2007 as a Microsoft Research project, with early partners including astronomers and educators from Caltech, Harvard, Johns Hopkins, Northwestern, the University of Chicago and several NASA facilities. Over the past eight years, millions of people have downloaded and used WorldWide Telescope, coming to rely on its unified astronomical image and data environment for exploratory research, teaching and public outreach.
WorldWide Telescope was designed with rich interactivity in mind. Guided Tours, which are especially popular among educators and astronomy enthusiasts, offer scripted paths through the 3D environment, enabling users to view and create media-rich interactive stories about anything from star formation to the discovery of the large-scale structure of the universe.
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Direct to WorldWide Telescope on Github
See Also: WorldWide Telescope Features