Android/iOS: Most photo editors for your smartphone come with the same features: colour correction, maybe a few filters and basic cropping. SKRWT adds something new with a ton of perspective correction tools. SKRWT allows you to adjust the perspective of your photos with a variety of tools. You can also correct some common lens distortions, like the fisheye effect you see on GoPro footage. The app is $1.49 on both platforms.
SKRWT [iTunes App Store]