This one is free right now as well. And; the 2 iaps are free as well. This is one of my favorites. There are many effects to play around with. Lens Light Visual Effects https://itunes.apple.com/app/id419518259
Camera + is a great camera app, but also has a great photo editor. Enlight is a great app and also was a top pick by Apple not long ago. PhotoForge2 is maybe one of the best, but I am not sure it is available anymore.
ACDSee has been in the photo editing business a long time. They offered all the IAP free a few months back, might happen again, but the basic editor is also good.