PNGGauntlet squeezes the last bit of size out of them. Furthermore, no information is lost during this process - the only thing that changes is the file size. Just select the files you want to optimize (or drag them onto the window), select where you want them to go, and click the button. PNGauntlet can also be used to convert JPG, GIF, TGA, PCX, and BMP files to PNG.