(Image by Muhammad Mahdi Karim CC BY-SA 3.0)
Stay Focused (free with in-app purchases) is an interesting app that does a very complex function for photographers called Focus Stacking. You take a series of photos, from 2 to 100, with different focus points selected. Then your photos are sent up to the developer server, and returned to you with all points of the photo in focus. This capability is really important when doing macro-photography and other focus-intensive photography, like wanting objects up close and in the far distance in focus.
Using the app is not as simple as pushing a button, but instructions are provided on the first screen and a detailed tutorial follows. I was able to take some pictures that gave me the equivalent of nearly perfect depth of field, meaning objects up close, in the mid-range, and in the distance were all in focus. Stay focused is certainly not a simple point and shoot. There are controls for manual exposure and color, live previews of the extremes of the focus range, and many options for sharing your photos.
The uploads can take a few minutes, and the app does not currently upload smoothly in the background, but a fix is coming for that. When the server has processed your photo it gets downloaded back to you. The app gives you 10 uploads to try the service out, then wants to sell you additional uploads at a price: US$0.99 for two or $4.99 for 15 uploads. Over time, that is going to run into money.
What the app does is impressive, and photographers are going to be really appreciative of what has gone in to making the app work. On the other hand, a casual photographer isn't going to want to keep paying to upload images, and a pro may have other software approaches to doing this with a DSLR. Zerene Stacker ($89) and Helicon Focus (pricing from $30-$240) both run on OS X. If you plan to do a lot of focus stacking, the Mac options might be more economical.
Stay Focused worked well, and it is pretty amazing to do this work on an iOS device, even if it requires an upload to create the final image.
Stay Focused requires iOS 8 or later.