Gravit
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... Gravit uses OpenGL with Lua, SDL, SDL_ttf and SDL_image. ... At any stage you can rotate your view in 3D and zoom in and out. ... It records the history of each particle so it can animate and display a path of its travels.
http://gravit.slowchop.com/dist/gravit-0.4.2-win32-installer.exe - 830Kb - Download - Screenshot