Splashy - Breathtaking, auto changing wallpaper app for macOS, Windows, Linux, iOS & Android
Unsplash Wallpapers for Mac (Official) - Curated, HD desktop background photos from Unsplash.
Wallcat - Enjoy a new, beautiful wallpaper, every day.
Wallpaper Wizard - Wow-worthy backgrounds for Mac
John's Background Switcher - Switch backgrounds to trending imgur, reddit, tumblr threads
Variety Wallpaper Changer - Variety is a wallpaper changer for Ubuntu which is featureful, yet slim and very easy to use.