I use Snapseed on Android. It's a practical app with many photo editing tools
I like how I can edit my photos here,
PhotoDemon - Lightweight portable BSD licensed photo editor for Windows focused on performance and usability.
VSCO - VSCO® is an art and technology company empowering people everywhere to create, discover, and connect. CompanyVSCO® is a trendsetting art and technology company that .
PhotoFlare - Quick, simple but powerful Cross Platform image editor.
PicsArt - Explore 100,000,000+ awesome images and photos on the web
PixBuilder - Free Photo Editing Software for PC
Pixelmator - Pixelmator is an image-editing application for Mac and iPad.