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.
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.