Awesome
Voxelmetric
Voxelmetric an open source voxel framework for unity3d. It's meant to be an easy to use, easy to extend solution for voxel games. Voxelmetric is currently in alpha so expect breaking changes and incomplete documentation. I am currently maintaining it alone and making changes as I learn but if anyone else wants to help they should feel free to make a pull request. Also use the issues to highlight bugs and suggest features.
For more information and documentation visit AlexSTV.com - Voxelmetric
Features
Terrain Generation
Generate realistic looking terrain with caves and landmarks like trees.
Ambient Occlusion
Darkening in the corners between blocks makes the terrain look more realistically lit.
Saving and Loading
Save and load your changes to the world at will.
Infinite Terrain
Terrain generates around a given object and is removed when you move too far away, there are no borders or limits.
Threading
Threading chunk updates and terrain loading means the voxels take full advantage of your hardware to generate fast without hurting framerate.
Define New Block Types
Define new blocks in the scene with your own textures and even your own 3d mesh for the block's geometry.
Pathfinding
3d voxel aligned pathfinding for units makes it possible for AI to move around the terrain.
Development
Voxelmetric is in development and is not yet at a 1.0 release, this means things are liable to change fast without notice or be broken and documentation will struggle to keep up.