Mooncraft -> Free
I just found this over the weekend. The full game is free with an ad that's kind of intrusive but can be removed for $2.99.
I've never been able to play Minecraft because my computer isn't very good, but from what I've seen in screen shots, this is set up pretty similar. There's two modes, Creative & Explore. Creative mode gives you all of the different types of blocks so you can experiment with crafting and building. In Explore mode you have to mine all of the blocks that you want to use.
I think it's worth a check out for free. Plus, I can't figure out some of the more complex crafting and hope more people discussing it will help figure it out.