The PrEdiTer project:
The project currently creates a procedurally generated terrain using Brownian Fractal noise (Several octaves of perlin noise added together).
The engine generates a planet of a given radius. More accurately it generates the sections of the planet as you walk around. It simulates a sun that rotates around the planet (a simplification of the actual physical model of a planet revolving around a sun).
The other major goal is editable terrain. The terrain is generated by the density function, but is actually stored and displayed from discrete voxels. This allows it to be 'dug' through at any given point.
The terrain also supports a variety of materials, as well as biomes that are oriented in the way a planets' would be - polar biomes at the north/south pole, and desert at the equator.
Further work on this project involves allowing building of custom building blocks, and procedural and flowing water.
Please check out the main page for technical updates and a link to the demo.