I've been involved in an effort to create a open source Minecraft starter package, with Unity, in the Gossip forums here:
In a nutshell, it provides a foundation for creating games similar to Minecraft. It's not an attempt to clone Minecraft. My hope is that it will encourage those who have played Minecraft, and want to learn or create something with their own ideas.
I figured it was time to move it to a dedicated home, on SourceForge. The site is brand new, as is my experience with SouceForge, so it's still getting some content. In the meantime, it has links to the downloaded Unity source, and the web player.
Here is the SourceForge link:
Here's a web player link for the current version:
I'm looking for community involvement to make it even better. It is and always will be a starter package, a template. It's not intended to evolve into a full blown game...that is for others to do, taking the package and adding their own unique and cool ideas. My intent is to provide the basics (infinite terrain, trees, lighting, some basic ai for creatures) so people don't have to keep reinventing the wheel.