This is a planetary (or any other object) simulator which makes use of Newton's Law of Gravitation to show the positions of the planets as a function of time. The simulation parameters can be edited, and planets/objects can be added and removed. The accuracy of the simulation is totally dependent on the "timestep" parameter.
Here are the currently available starting configurations:
Not working? This application requires Java plug-in.
You can get Java from http://java.sun.com/getjava.