World Generators

Fractal Mapper
Commercial program to draw various maps for fantasy roleplaying games. Includes an add-on that allows simulation of climate and erosion effects.
http://www.nbos.com/products/mapper/mapper.htm

Fractal Planet Generator
A web interface for Torben Æ. Mogensen's fractal based planet generator. Produces PNGs only.
http://www.eldritch.org/erskin/roleplaying/planet.php

Fractal World
A Windows program to generate a planet's geographic features from fractal algorithms.
http://raieh.homelinux.net/cgi-bin/raieh.pl?FractalWorld

Fractal Worldmap Generator
Creates fractal world maps in .GIF format.
http://www.lysator.liu.se/~johol/fwmg/fwmg.html

Terranova: Planet of the Day
Generates .GIF and .JPG images of planets.
http://www.fourmilab.ch/terranova/terranova.html

Wilbur
An outstanding fractal-generating world mapping tool. Current development copy is freeware, and available for download. Instructions for interfacing with Campaign Cartographer 2 are included on the site.
http://www.ridgenet.net/~jslayton/software.html