The fractal world generator is based on code by John Olsson. The donjon version was completely rewritten in Nov 2009, and includes changes to the faulting algorithm and support for alternate color palettes. It also supports additional map projections; icosahedral was added in Sept 2010, and sinusoidal, Mollweide, and transverse Mercator in Aug 2011.
A sphere is bisected along a random great circle, and one half elevated above the other. Repeating this process thousands of times produces a faulted terrain. Next, the elevation values are sorted into a histogram to determine sea level. Finally, the elevation map is scaled into a color map, and transformed into the desired projection.
The original code has a few minor errors which can cause a segmentation fault and crash. Version 2.2a linked below fixes these problems. Both versions are provided under the GNU General Public License, version 2.
worldgen 2.2, by John Olsson
worldgen 2.2a, fixed