Gravit is a gravity simulator which runs under Linux, Windows and Mac OS X. It's released under the GNU General Public License which makes it free. It uses Newtonian physics using the Barnes-Hut N-body algorithm. Although the main goal of Gravit is to be as accurate as possible, it also creates beautiful looking gravity patterns.

Welcome to the nanoworld of the Pixel Paradox universe of 2099 AD. Geo Gizmo is a pollution-free nanodevice that acts as a perpetual-motion machine to generate electricity from artificial gravitons in motion above a quantum energy plate, without any loss of kinetic energy. However, not only is it functional, it's also a marvelous work of art. Gee whiz, it's a Geo Gizmo! Disclaimer: This screensaver, Geo Gizmo 3D, does not generate electricity.