A Galton board is a vertical board with n rows of pegs onto which a ball is dropped.   Each time a ball hits a peg, it has a probability p of bouncing to the left and a probability of 1-p of bouncing to the right. The simulation's histogram shows the distribution of x-coordinates as the balls leave the board and are collected into bins.
The simulation gives rise to the binomial distribution if the probabilities of left and right bounces are equal. At first there does not seem to be any pattern but after many trials the familiar "bell curve" shape begins to emerge.

Please note that this resource requires at least version 1.5 of Java (JRE).