Gravity.app is a program, written in Objective-C for the Mac, that simulates Newtonian Gravity between any number of circles on a 2D plane.

The Gravitational Constant has been changed from 6.11x10^-11 to 6.11x10^-1 to allow for the effects of gravity to show more drastically to the user (otherwise, almost nothing seems to happen).

A cool way to use the program is to create two objects, one with a mass of 1000, a position of (0, 0), and a velocity of (0, 0), and another with a mass of 0, a position of (100, 0), and a velocity of (0, 2.5). This results in a near-circular orbit.