Crunch is a tool for lossy PNG image file optimization. It combines selective bit depth, color type, and color palette reduction with zopfli DEFLATE compression algorithm encoding using the pngquant and zopflipng PNG optimization tools.

This is a free software web service that allows you to generate maps of cities using OpenStreetMap data. The generated maps are available in PNG, PDF and SVG formats and are ready to be printed.

PunyPNG is a free website optimization tool that dramatically reduces the file size of your images without any loss of quality.

Pngcrush is an optimizer for PNG (Portable Network Graphics) files. It can be run from a commandline in an MSDOS window, or from a UNIX or LINUX commandline.

Its main purpose is to reduce the size of the PNG IDAT datastream by trying various compression levels an PNG filter methods.

better PNG background-image support in IE6