Pixels slowly rain down and fill up your screen. Background color adapts to your theme. If my math is correct, should take 9 hours to fill your screen.
Edit: update now available -- it's 9x faster!
To save as wallpaper:
load #pixel_rain-1
then
save /appdata/system/wallpapers/pixel_rain.p64.png
(/appdata/system/wallpapers must exist)
My first Picotron cart!