Cell phones have a small aperture, hence a large depth of field. In other words, most of the scene is in focus at once. However, if you record video while moving the phone slightly, and you add the frames of the video together, you can simulate the large aperture of an SLR. This app lets you do that.
Adding together many frames has a side benefit; it gathers more light. Thus, pictures you take with this app will be less noisy than pictures taken with the iPhone's native Camera app. The app allows you to do many other things, like see through bushes, remove moving people or cars, blur flowing water, and simulate a tilt-shift lens, but let's not get ahead of ourselves. Try the app!
You can also look at some Screenshots, Example photographs, a special section on Version 2.0's Multi-point and tilt-shift focusing effects, and a Tutorial on how to use the app. For a more visual tutorial, check out these two Videos. For release notes on each version, and a list of known issues (i.e. bugs), click on Support & version notes. If you want to quickly leaf through the images from this web site with minimal captions, I've loaded them into this Google Photos album. Oh yes, and here's some publicity about the app.