I've been playing some Terraria with friends and kids. Its a fun game so I looked to see if there are any good open source clones. I looked at a few but none are very far along.
Terrarium is one I looked at. I'm not sure if mining is implemented. I didn't find the key for it at least. It is a pain in the neck to build. I had to do some modifications to build with the latest box2d. I do really like the frog blob sprite.