Stellarium is a free open source planetarium for your computer. It shows a realistic sky in 3D, just like what you see with the naked eye, binoculars or a telescope.

The free space simulation that lets you explore our universe in three dimensions

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!