SpaceEngine - is a free space simulation software that lets you explore the universe in three dimensions, starting from planet Earth to the most distant galaxies. Areas of the known universe are represented using actual astronomical data, while regions uncharted by human astronomy are generated procedurally. Millions of galaxies, trillions of stars, countless planets!
PC version available. Uses mostly OpenGL, so there might be hope for Linux and OS X (if they update their OpenGL version) front-ends in the future as well.
Usage example:
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