John's Background Switcher - Switch backgrounds to trending imgur, reddit, tumblr threads
Wallcat - Enjoy a new, beautiful wallpaper, every day.
Variety Wallpaper Changer - Variety is a wallpaper changer for Ubuntu which is featureful, yet slim and very easy to use.
Splashify - Beautiful desktop wallpapers for Mac and Windows
Wallpaper Cycler - NuonSoft WallpaperCycler is a powerfull utility to manage all your wallpapers and to automatically cycle between your wallpapers.
Irvue - (previously Unsplash Wallpaper) Gorgeous wallpapers on your Mac.