Guide to the Galaxy - Stella 2000
[Win 9x/Me/NT/2000 shareware] Mixes sky simulator and astronomical encyclopedia with speaking guide. Simulates most aspects of the space-watching experience. Other free astronomy software included.
http://www.stella2000.com

Sky3D
[shareware - Win95/98/NT] Offers realistic views of entire sky with interactive and three-dimensional view modes.
http://www.sky3d.com/

Solar Kingdom
[commercial, demo available - Win95/98/NT] A solar system simulator and planetarium, with planetary encyclopaedia.
http://www.silverfrost.com

OpenUniverse
OpenGL] Newest NASA data creates a fast 3D display of our home solar system, 25000 stars, galaxy, planets, moons, asteroids and even controllable spacecraft.
http://www.openuniverse.org

Solar System Applet
[online Java applet] This 3-d solar system applet can be rotated and zoomed with the mouse. Below it are links to other online gravity simulators and resources for building solar system simulations.
http://www.burtleburtle.net/bob/physics/solar.html

Xstar N-body Solver
[open source - Unix] Displays results to the screen or can be used as a screen saver. Includes a college level introductory text on the n-body problem.
http://www.midwestcs.com/xstar/

Starry Night
[commercial - Win95/98/NT, Macintosh] A planetarium and solar-system simulator; lets you view the universe from anywhere in our planetary neighbourhood in the past, present, and future.
http://www.starrynight.com

Virtual Galaxy Project
to and around nearby stars in the Milky Way Galaxy.
http://www.ccm.net/~jrsmith/index.html

Orrery
[commercial - Acorn/StrongARM RISC OS] An orrery is a physical or virtual model of our solar system.
http://www.photodesk.ltd.uk/space/orrery/index.html

Gravel
[freeware - Windows] Models the interaction between bodies in space according to Newtonian physics.
http://www.rcl-software.org.uk/gravel/

Gravel
Free simulation software which models the interaction between bodies in space according to Newtonian physics.
http://homepage.ntlworld.com/rcl-software/gravel

GrandTour
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.
http://www.faithreason.org/grandtour

3D Solar System Simulator
A Java applet that shows an interactive 3D representation of the planets and satellites of the solar system.
http://www.inicia.es/de/avillanueva

SpaceWander Virtual Space Trip!
SpaceWander's award-winning multimedia tour of the Universe features real space pictures from NASA
http://www.spacewander.com

Space simulator and 3d engine tutorials
Space simulators reviews and tutorials to program a 3d engine for a space sim.
http://www.spacesimulator.net

Celestia
A free 3D space simulator that lets you travel through the solar system and beyond to over 100,000 stars. [Windows, Mac; Open source]
http://www.shatters.net/celestia/

StarStrider software 3D planetarium
[shareware - Win 98/ME/2K/XP] A 3D software planetarium. Photo realistic real-time 3D renderings of 2 million stars, galaxies, nebulae, and the Milky Way. Includes several educative tutorials.
http://www.starstrider.com/

AstroFly
[freeware - Win 98/ME/2000/XP] Three-dimensional models of the Milky Way neighborhood.
http://www.anumajor.com/astrofly/index.html

Gravity Simulator
[freeware - Win 9x/NT/2k/XP] Simulates orbits of planets and other celestial bodies.
http://www.orbitsimulator.com/gravity/articles/what.html

Liftoff Space Simulator
[commercial - Windows] Hands-on presentations and simulations about being an astronaut and commanding the space shuttle.
http://www.eti-tech.com

Copernic space simulator
A freeware program that lets you navigate through the solar system neighbourhood at different times in past or future, and to see the sky in a stereographic projection.
http://www.geocities.com/fmarc83/paginigpu/ecopernicus.htm