ImageOptim - Faster web pages and apps.
Faviconer - Faviconer.com, or favicon generator, is online tool for creating favicon.
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.
Online Image Converter - Online Image Converter converts your BMP, JPG, PNG, GIF or ICO files quickly and easily.
Minuimus - Transparent automatic compression of a wide array of file types, using well established open source utilities.
Ordinatore - Those who want to tidy up their Macs will surely love this application.