ImageOptim - Faster web pages and apps.
Ordinatore - Those who want to tidy up their Macs will surely love this application.
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.
ConvertIcon! - Converticon is a simple icon utility.
Minuimus - Transparent automatic compression of a wide array of file types, using well established open source utilities.
GenFavicon - Generator Favicon.