Fondo is described as 'Find a variety of the most beautiful wallpapers from Unsplash.com the world’s most generous community of photographers' and is an app in the Photos & Graphics category. There are four alternatives to Fondo for Linux and Mac. The best alternative is Variety Wallpaper Changer, which is both free and Open Source. Other great apps like Fondo are QuickWall (Free, Open Source), Desktopnova (Free, Open Source) and BackStory Wallpapers (Paid).
QuickWall was initialy launched as a wallpaper app that would set wallpapers directly from the commandline. Later due to a lot of requests from users , a theme option was added which uses pywal to generate themes from the wallpapers.
This application brings a little variety onto your desktop! It changes your desktop wallpaper automatically after a preset period of time. At the moment it works with a Gnome and Xfce based system. Maybe other desktop environments will be supported in the future.
BackStory Wallpapers uses the photos in your Photos library to create beautiful backgrounds for your desktop. Select an arrangement, some albums, and maybe a filter or two. Then set the timer and let BackStory show you collages of images.