Gridditor is an image effects app that smartly uses a gridlike interface to let you swipe through the intensity of each filter, but it's lacking some features found in other apps from this genre.
Like other photo effects apps, you can snap a fresh picture with your iPhone camera or choose one from your photo library. In Gridditor, the photo you use will be the focal point and you can choose four effects (from 22 total) in each cardinal direction. As you swipe farther out in one direction, the filter for that side gets stronger. With this interface, it means you can easily blend effects and know just how much you're getting from each effect.
For more fine-tuning, when you find an effect you like, you can touch the check mark in the lower-right corner to make the effected image your focal point. Now you'll be able to experiment with a new set of effects in each direction (including Focused, Focused Color, and Focused Contrast) that use your originally chosen effect as the starting point.
When you're finished, the app uses the standard iOS 6 sharing button setup so you can save to your Camera Roll, send through e-mail, post to Twitter or Facebook, and more. But you also have the option to perform further edits in supported apps. On my iPhone, PhotoToaster shows up as an option for export.