ImageOptim decreases the file size of PNG, JPEG, and GIF images, even those "Saved for Web". It combines OptiPNG, PNGCrush, AdvanceComp, PNGOUT, Jpegoptim + Jpegtran, and Gifsicle for the best possible optimization.
IMGCrush is an image compressor. IMGCrush_GUI is a simple GUI for IMGCrush. IMGCrush can perform both lossy and lossless compression in order to achieve the file size or quality that the user requires.