It is designed for mac os x, but you can use it on Windows too. The icon is empty because it's purose is to "overlay" the icon stacks (it "inserts" the icons behind it as if they were inside the "wooden stack icon"0.
To be honest, I didn't use Your wall on iconpaper. It has been put there by =Gor0n I guess, which was kinda a surprise for me. I don't mind it though; Your wall was an obvious inspiration for the preview image I've made. Maybe I'll even transform it into the full wallpaper, in which case I'll mention You in the description .