ImageOptim is a GUI for lossless image optimization tools: Zopfli, PNGOUT, OxiPNG, AdvPNG, PNGCrush, JPEGOptim, Jpegtran, Guetzli, Gifsicle, SVGO, svgcleaner and MozJPEG. All Free and Open-Source. It removes bloated metadata, saves disk space & bandwidth by compressing images without losing quality. It is lightweight, easy to use, support drag-n-drop. Since it compress your images on local computer without uploading to a remote server, the compression speed is extremely fast.
It 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).
ImageOptim removes EXIF metadata, such as GPS position and camera’s serial number, so that you can publish images without exposing private information (but there’s an option to keep the metadata if you need it).
You can choose to download it from its official site here or get it from GitHub here. Note that ImageOptim is not available in Mac App Store. Please beware of knock-offs in the App Store! Apple’s has been selling three already.