This is an unofficial National Geographic app that allows you to view the current and past photos of the day.
You can add a widget to your home screen so that you can see the latest photo, choose your favourite past photo, and set your favourite photo as your wallpaper or let the app automatically choose a new random photo every hour.
It is cool if you have a meeting at your place like a dinner or so, and turn on your TV and let the app to randomize images. Your TV turns into a big photo frame with pictures of nature and scenes from around the world.