It has the following unique features.
1) It keeps track of and displays your progress.
2) It has search functionality (show all prime questions?)
3) It allows you to submit a solution to any problem.
4) It auto updates problems that change and even downloads new problems when they become available.
5) Its backward compatible as far as Android 2.2.
6) It has Facebook integration which allows you to post about your success whenever you solve a problem.

I built this app because in my first week of being a Eulerian, I became really addicted to the website. I was trying to plan my next problem each morning during my bus ride to work. I even ended up printing the first 50 questions. So I wrote this app to make it easier for me to keep track of my progress, to help me plan my next problem and to save trees.

Source code available on GitHub: https://github.com/ccoffey/ProjectEuler