Ruby-plasma-fractal is a project mainly written in Ruby, it's free.
A simple implementation of fractal terrain generation in ruby
This is a port of M. Jessup's Java implementation of the diamond-square algorithm to ruby. It also includes Chris Hadley's changes to the algorithm per the StackOverflow thread below.
Essentially generates a 2d array of values that can be used for height values in a terrain.
require 'lib/plasma_fractal' fractal = PlasmaFractal.new(:size => 9, :height_seed => 100) fractal.generate! fractal.display_height_map
100 99 115 108 101 117 128 122 100 99 108 108 101 112 114 111 117 99 122 107 117 114 89 101 119 124 122 114 102 114 104 85 105 113 120 114 96 102 108 96 89 91 99 98 96 102 112 107 112 117 101 95 98 102 106 91 95 116 118 110 106 112 106 99 99 114 116 114 116 121 109 99 100 99 115 108 101 117 128 122 100
The values are currently converted using to_i for display, so it's not 100% ready for use, if you want all the floating-point accuracy, it should be pretty easy to get at the data needed.