Digital Diva here. I just can't believe what some of these apps can do (along with the iPhone herself). The Dude and I were walking through a Sedona, Arizona canyon a couple months back. We came upon one of those impossible lighting situations that is now possible thanks to the great HDR apps.
By tapping on a given spot on your iPhone, you can tell it where to focus and where to figure exposure. So for the first photo I tapped on the highlight in the far canyon wall that was harshly lit. So you can see that but not much else. For the second shot, I tapped on the dark shadows in the creek area but the highlights then blew out. Two really poor exposures overall, because there's just too many stops of exposure to hold it.
Enter PRo HDR app and the third photo shows the combined HDR photo. I added a little warmth, sharpness, and saturation in Photoforge and Iris apps. (I also like TrueHDr app for some images - just a trial and error approach seems to work for some images.)