Crunch : Crunch is a tool for lossy PNG image file optimization. It combines selective bit depth, color type, and color palette reduction with zopfli DEFLATE c...
PunyPNG : PunyPNG is a free website optimization tool that dramatically reduces the file size of your images without any loss of quality.
Squoosh : Squoosh is an image compression web app that allows you to dive into the advanced options provided by various image compressors.
RoundPic : Online tool for making anti-aliased rounded corners (very Web 2.0!) for avatars and images
Caire : Caire is a content aware image resize library
Trimage is a cross-platform GUI and command-line interface to optimize image files via optipng, pngcrush, advpng and jpegoptim