Nbody is a small, simple application that simulates n-body gravitational motion of discrete masses using classic 4th-order Runge-Kutta integration. You can create simulations of up to 100 masses, or run and edit one of the built-in examples. The display of motion can be rotated and zoomed in 3-d while running.
All simulation data are saved when you quit the program, and are automatically reloaded next time to start from the same place. You can save edited simulations to disk or the pasteboard for export via email. Simulations can be downloaded from a website or via email as text. There is a built-in users manual, and a companion website with additional information.