There are so many photo-editing apps in the App Store it's hard to keep up, but I want to call PhotoPath to your attention. It's a free, universal app that can be, for many photographers, a one-stop solution for creating multi-photo presentations.
The app starts with a series of frame layouts. Pick the one you like, then tap on each frame to either add a photo from your camera roll or shoot one with the camera. You can scale the photo and move it around until you are happy with the composition. Then add some filtering like black and white, sepia or intensify the colors.
PhotoPath allows you to change the type of frame and borders, as well as adjust the size, color and border design. You can add a caption, which many photo apps don't include. It's a really nice app to have when you are sending images back from a vacation or party, because you get something "finished" and not just a series of photos. You can save the finished project to your camera roll, or email it. You can also print from your iPhone or iPad if you have a compatible printer.
The app is ad-supported, but I don't find the ads intrusive, and they come up only rarely. If you want to kill the ads, you can get the ad-free version for US$0.99.
The app contains help, but I found it intuitive enough that I didn't need the hints. More layouts and filters would be welcome, but you can create some nice image sets with what is provided. I don't consider PhotoPath a complete photo-editing app. There aren't all the features people will want, like sharpening and curves, but that isn't the point. PhotoPath allows you to create multi-photo compositions with some minimal but effective tools like frames and filters.
The app runs on any iOS device running iOS 6 or later, and is optimized for the iPhone 5. PhotoPath is a clever app, the price is right and the output looks great. I've added it to my permanent roster of photo apps.
I have some sample screens in the gallery.