World Builder

World Builder uses a more complicated algorithm than SimEarth. It begins with a single, flat landmass in the center of a square world. At each timestep there is a chance a landmass will split in two, and the parts will move away from each other for awhile, slow down, then reverse direction until they hit each other. Landmasses can split while they are already moving, and mountain ranges build up at the leading edge of any moving land. Also, at each timestep any existing mountain ranges erode a little, so that old mountain ranges eventually disappear.

The result is usually a world whose continents look like they could all fit together, the way South America and Africa look today. Mountain ranges, rather than single peaks, are created. It is also relatively simple to code, because faults are only used at the moment a landmass splits. After that, only the velocity of each landmass is tracked.

On the other hand, no island chains ever get generated, and erosion never progresses to the point that old land disappears, because there is no process to generate new land. Along with the lack of wraparound, which prevents pieces of the jigsaw puzzle supercontinent from ever changing places, this gives the generated worlds a look that always differs from Earth in the same characteristic way.

Of course, like SimEarth, there's a lot more being simulated than continental drift in World Builder. Once the user is satisfied with the continents, World Builder can calculate seasonal temperatures and rainfall, climate zones, rivers, and lakes, and then export the world into Nation Builder. It's a shame it's not available any more.