If you visit the worlds link, be sure to select "Show Options" and adjust the time of day. I'm assuming there are a lot of programmatic elements that create these effects.
A few years back, I used a few tools piecemealed together to make a living wallpaper from Ferrari's waterfall piece.
I'll now gladly pay to have it done properly. :)
Edit: Curses, no parallax! The version of waterfall I made has parallax scrolling, I worked very hard getting that working! (By which I mean I found one strange wallpaper tool from a Korean developer that is the only tool that worked to pull off parallax animated GIF wallpapers). On a 21:9 screen. waterfall is about 3 screens wide...