I have a huge collection of NASA photos taken from the Astronomy Pic of the Day Web site (http://apod.nasa.gov/apod/astropix.html) stored in a folder in my Dropbox. No matter what computer system I'm using, I rotate those images on my background, getting a virtual tour of the universe on every screen. Oddly enough, it can be challenging to get that image rotation to work well in Linux. I've mentioned some wallpaper-rotating applications before, but Slidewall is really pretty cool.

Slidewall includes a small dæmon process to change GNOME-based desktop wallpaper images. It's in the Ubuntu 12.04+ repositories, but it will work with any GNOME-based system. Rotating a wallpaper collection works well, but Slidewall goes the extra mile and will fetch collections live from the Internet, or it can display a live picture of the Earth showing which parts have sunlight and which don't. Slidewall is a huge step forward in desktop wallpaper management, and if you have a difficult time deciding what picture to use as your background, now you don't have to choose just one!