I was inspired by the many crappy de-makes of Minecraft to make my own. I'm not saying mine's not crappy, but it's not finished yet. You see, right now you can only place stone, I'm adding in other blocks right now - just wanted to get this out there as fast as I can.
Anyways, to create a new "level," just make a new folder, and choose that when you're loading a file. It uses the same building mechanics as the original Minecraft, so to build a block, it has to be connected to another block. Just like how in the real Minecraft, you can't just make blocks floating in mid-air right away. You have to build up, then break the blocks that surround it. Don't worry about that though - you have a bedrock floor to help you get started. Right click to place a block, left click to delete it.
Update 1 (4/8/11) - Added more blocks to place.
Update 2 (4/9/11) - Added lighting.
This game requires the .NET Framework 3.5 - and so only works on Windows. It was completely programmed in C#, and besides, if you don't have the .NET Framework 3.5, you probably aren't cut out to use a Windows computer.