ImageOptim is described as '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)' and is a popular Image Optimizer in the photos & graphics category. There are more than 100 alternatives to ImageOptim for a variety of platforms, including Windows, Web-based, Mac, Linux and Wordpress apps. The best ImageOptim alternative is ImageMagick, which is both free and Open Source. Other great apps like ImageOptim are Caesium Image Compressor, FileOptimizer, OptiImage and TinyFast.