I wrote Catfood Desktate after I discovered NASA's Blue Marble images. I used a couple as desktop wallpaper and then decided that I wanted something more dynamic and the first version of Desktate was born in 2003. The name is a combination of Desktop and rotate because initially Desktate just wrapped the image so that it was always noon at the center of the screen. It isn't a brilliant name, but it stuck.
That first version got a little boring, so I updated it to calculate the distribution of sunlight and night across the surface of the earth. Later I also added cloud cover into the mix using a near realtime composite image that gets updated every three hours.
The current version of Desktate uses the monthly global images from NASA, interpolating the images to produce a daily estimate of snow and ice cover. This is pretty subtle - see a year in twelve seconds to see this feature in action. I'm working on a new video that will also show cloud cover over the course of a year.
There's now a lot that can be customized in Desktate. See the layers page to get some idea of the possibilities.
I like the fact that Desktate makes it easy for me to gauge the time for day for friends and family around the world. It's also nice to see the seasons change throughout the year.