ImageOptim - Faster web pages and apps.
TinyPNG - Make your website faster and save bandwidth. TinyPNG optimizes your PNG images by 50-80% while preserving full transparency!
OptiPNG - OptiPNG is a command-line PNG optimizer that recompresses image files to a smaller size, without...
Oxipng - Oxipng is a multithreaded lossless PNG compression optimizer. It can be used via a command-line interface or as a library in other Rust programs.
TruePNG - Command-line PNG optimizer.
Caesium Image Compressor - Compress your pictures up to 90% without visible quality loss.