Variety Wallpaper Changer - Variety is a wallpaper changer for Ubuntu which is featureful, yet slim and very easy to use.
Wallpaper Wizard - Wow-worthy backgrounds for Mac
Splashy - Breathtaking, auto changing wallpaper app for macOS, Windows, Linux, iOS & Android
Wallcat - Enjoy a new, beautiful wallpaper, every day.
Unsplash - Unsplash is a website with high-quality free HD images. It has a catalog of more than three hundred thousand striking images that are neatly organized with tags. Read more about Unsplash.
WLPPR - Beautiful mobile wallpapers made from satellite imagery