Title: Crop
Cost: Free, with $ 1 in-app purchase to remove ads and maintain aspect ratio
Platform: iOS
Sometimes an app is so simple, but works so well, it's hard to imagine how you would get along without it. For me, one of those is Crop by Green Mango Systems.
Whether it's focusing on the content of a screen-captured Instagram post or creating a quick thumbnail for an avatar, there are many occasions when you'll want to remove the bulk of an image or rotate it on the fly. You simply select the image, use the eight points of the image canvas to determine the size you want, and you can keep finessing things until you hit "Save." And unlike the crop option within the iOS photo roll, Crop saves your creation as a new file, so you don't loose the original.
In a digital photography workshop at our state edtech conference this summer, the presenter, Leslie Fisher, emphasized taking pictures from where you stood and cropping them instead of using the digital zoom feature in your device camera. She said that results in less degradation of the image quality. Crop is super-useful for anyone adopting that sort of digital photography workflow.