I don’t have an app that would generate a billion dollar in revenue, but perhaps be useful to atleast a few that I know of, including me. Here is one more - NASA Image of the Day IOTD app.
This app fetches the NASA Image of the day from their RSS feed, and shows you just 1 image per day. However, it puts the last 6 images that you viewed using this app to the localstorage. You can share the picture, set as your lockscreen right from the app itself. Give it a try, and let me know what you think.
Download it from here.