A free tool that adjusts your wallpaper on a timer
SunsetScreen is a simple tool that contains a series of sunrise and sunset wallpapers. It displays each on a timer so that your wallpaper appears to transitions from sunrise to sunset. For example, you may have the sun setting at 10pm and have it rise at 7am. The main reason for this app is to change your background colors over the course of a night, which is not great because you shouldn't leave your computer on all night.