ImageOptim is excellent for publishing images on the web (easily shrinks images “Saved for Web” in Photoshop). It's useful for making Mac and iPhone/iPad applications smaller (if you configure Xcode to allow better optimization).
Oxipng is a multithreaded lossless PNG compression optimizer in Rust. It can be used via a command-line interface or as a library in other Rust programs.
Experimental, fast Web PNG/JPG optimizer which offer lossless, visually lossless or lossy compression. it performs image reductions over iterations thanks to recursive multi-processing and multithreading systems.
OptiPNG is a command-line PNG optimizer that recompresses image files to a smaller size, without losing any information. This program also converts external formats (BMP, GIF, PNM and TIFF) to optimized PNG, and performs PNG integrity checks and corrections.
-Combines PNGOUT, OptiPNG, and DeflOpt to create the smallest PNGs -No image quality is lost — only file size -Converts JPG, GIF, TIFF, and BMP files to PNG -Ultra-configurable
PNGGauntlet is a .NET program that uses Ken Silvermans PNGOUT, OptiPNG and DeflOpt to optimize PNG fil.
Curtail (previously ImCompressor) is a useful image compressor, supporting PNG and JPEG file types. It support both lossless and lossy compression modes with an option to whether keep or not metadata of images. It is inspired by .This app doesn't have any features at the moment.