E-mage - From developers to developers: a cross-platform tool for losslessly image compression.
TinyPNG - Make your website faster and save bandwidth. TinyPNG optimizes your PNG images by 50-80% while preserving full transparency!
Optimus.io - Lossless image optimization
JPEGmini - JPEGmini - The Photo Optimization Tool Trusted by Tens of Thousands Image Perfectionists
OptiMole - Optimole makes your images weigh even 80% less while looking just as good!
ImageOptim - Faster web pages and apps.