FlixAPix (free) is an innovative app that lets you take a pair of photos and add an interesting transition between them. In-app purchases offer additional transitions. Photos can be captured live from within the app, or you can import from your camera roll.
You can sign up for a free account, but it isn't required. All the rendering is done off your device on a remote server. With an account a space is created with all your animations. Without an account, they are still there but you may have to search among all the other unregistered people creating animations. Your photos remain private and are not viewable to others.
FlixAPix for iOS
I gave the app a try with a couple of scenic shots. All you have to do is select them, and the app does the rest. You can have sound effects or not. The included animation is a zipper, and the zipper is pulled down to reveal your second photo. The rendering was pretty fast, under a minute. My only issue is that each transition beyond the included one cost US$0.99. There should have been a couple samples included rather than just one. If you decide to get all the animations, which total 22, the app would get expensive. Some of the animations are creative and high quality, but the developer should include some multiple transition packs at a low price, rather than price each animation separately. Better still, charge a buck or two for the app and include 4-5 animations. Many of the paid EFX, like water droplets and falling leaves are really quite attractive. The included zipper effect, not so much for my taste.
I like the idea behind FlixAPix. Your animation can be saved as a QuickTime movie to your device and freely shared.
FlixAPix requres iOS 6 or later. The app is not universal, so it is best suited to the iPhone or iPod touch.