Astronomy software program that allows you to simulate how astronomical objects move and interact under the force of gravity.[Commercial, free demo, multilingual]
[Freeware - Win3.x/95] A three-dimensional aid to viewing some of the nearer stars of our galaxy, navigating the distances between them, and accessing basic stellar information.
A freeware program that allows the user to navigate through the solar system neighbourhood at different times in past or future and see the sky in a stereographic projection.
Accurate wireframe simulator for the Voyager and Giotto space missions, with animation capability. Developed at JPL for science/navigation, and filmed by the BBC/NOVA. Conveniently runs from any Windows/DOS. Freeware.
[open source - Win95/98/NT/2000 or Unix/Linux and OpenGL] Newest NASA data creates a fast 3D display of our home solar system, 25000 stars, galaxy, planets, moons, asteroids and even controllable spacecraft.
ORBITER is a free flight simulator that goes beyond the confines of Earth's atmosphere. It is not a space shooter, and aims to be as realistic as possible.