Where can you download free astronomy software?

Stellarium is awesome! I wish I could install it on everybody's computer:

The best site to download free astronomy software is: Shatters. Celestia is THE BEST universe navigation program I have ever seen. It is like Google Earth, but for thousands of solar and extra-solar objects. It's easy to use and the graphics and navigation is amazing. There you can download add-ons to the program, adding to the universe. You can even tweak the universe to what you want it to look like!