Worlds is a voxel game with programmable terrain/biomes and custom textures, blocks, items, character models, etc. A game in which you create your world. You start with textures, then make blocks from them, then you write rules to distribute these blocks over your landscape. Totally infinite possibilities.
A update that adds ability to load and share worlds more easily. Please don't forget that in order run the game you'll have to install .NET 4.0 and XNA 4.0 Redistributable