ImageOptim(http://imageoptim.com/) : ImageOptim optimizes images — so they take up less disk space and load faster — by finding best compression parameters and by removing unnecessary comments andcolor profiles. It handles PNG, JPEG and GIF animations.
PNGOUT (http://www.advsys.net/ken/util/pngout.htm): PNGOUT is a tool which can optimize PNG files created by other programs. It can be run from the Windows Run dialog box or at the command prompt. PNGOUT can produce even smaller files thanpngcrush -brute or optipng -o7, however, since PNGOUT does not automate trials, you will have to find the right options yourself (Note:PNGOUTWin supports trials).
extended OptiPNG (http://optipng.sourceforge.net/) : OptiPNG is a PNG optimizer that recompresses image files to a smaller size, without losing any information. This program also converts external formats (BMP, GIF, PNM and TIFF) to optimized PNG, and performs PNG integrity checks and corrections.