This is a simple, low graphics online game called Falling Sand. It is highly addictive in a hypnotic sort of way. Rather than try to explain it, just try it out (it's a Java applet).
BTW, the real point of this post is to test the integration between Digg and TypePad...I just thought I'd make it fun! While you're there, also try the Hell of Sand version. You can try different versions using the links across the top of the page.
