Thought some people here might be interested in this. It's a system for generating huge block-based worlds, with the blocks stacked in layers, allowing the formation of rivers, hills, mountains, and other vertical structures. It currently features some cool dynamic block-based animation of both water and trees, and it does some basic shading to create shadows around blocks stacked up in higher layers. It has support for drawing animated grass on top of the grass blocks, but I don't have any good images to use for it yet so I disabled that in the video (it's not disabled in the source version).
Feel free to fork, clone, etc.