Wallcat - Enjoy a new, beautiful wallpaper, every day.
Virtual Museums - Explore the world's museums, virtually.
Splashy - Breathtaking, auto changing wallpaper app for macOS, Windows, Linux, iOS & Android
Louvre Museum Online - Explore the entirety of the Louvre's collection for free
Irvue - (previously Unsplash Wallpaper) Gorgeous wallpapers on your Mac.
Sketchfab for Museums - Browse thousands of cultural artifacts in 3D and VR