Optimage - Advanced image optimization tool
Pixlr - Pixlr® makes it easy to transform everyday images into stunning works of art.
ImageOptim API - Web service for image compression
Photoscape - high quality photo editing software, that enables you to fix and enhance photos.
Imagify - Optimize and resize images online and through your CMS.
Fotor - Fotor is an all in one visual platform. It includes photo editor, collage maker, and graphic designer. You are free to make a visual look more beautiful.