Microsoft WorldWide Telescope

Microsoft WorldWide Telescope screenshots

A virtual telescope that lets you browse though the known universe
Guided Tour
Microsoft WorldWide Telescope 2.1 : Guided Tour

Alternative downloads

Universe Sandbox
Create and destroy planets, solar systems, galaxies, or even galaxy clusters.
Alcyone Astronomical Tables
Alcyone Astronomical Tables provides various astronomical information.
World Wide Telescope
Install WWT and start your explorations in space and earth.