Cost: Free
Available for: Apple iOS and Android
PicsArt is one of the most sophisticated photo applications for the smartphone. I have found versions for Android and iOS smartphones. The app includes five modules: Picture Editor, Magic Effects, Draw, Sharing, and Photo Art Community. Picture Editor is the central module of the application. It editing photos at will. PicsArt offers primary effects such as crop, rotation, cropping, desaturation.
There are more sophisticated tools: sliders for contrast, saturation, color swap, selective desaturation, brightness, etc. Works on layers (yes!) Allows you to overlay other images or textures on the original photos. Each layer can be edited independently, including contrast and opacity.