John's Background Switcher - Switch backgrounds to trending imgur, reddit, tumblr threads
WLPPR - Beautiful mobile wallpapers made from satellite imagery
Variety Wallpaper Changer - Variety is a wallpaper changer for Ubuntu which is featureful, yet slim and very easy to use.
Muzei - Muzei is a live wallpaper that gently refreshes your home screen each day with famous works of art.
Splashify - Beautiful desktop wallpapers for Mac and Windows
Artpip - Artistic wallpaper for your desktop, refreshed daily.