ImageAlpha!

ImageOptim is excellent for publishing images on the web (easily shrinks images “Saved for Web” in Photoshop). It's useful for making Mac and iPhone/iPad applications smaller (if you configure Xcode to allow better optimization). ImageOptim removes EXIF meta­data, such as GPS position and camera's serial number, so that you can publish images without exposing private information (but there's an option to keep the meta­data if you need it).

Saving images for web/email/other media with the best compression ratio and quality is a difficult task if you don’t have the right tools. Choosing the right format then choosing the right parameters are the key factors of smaller files. Previewing the resulting image and the projected filesize will help the user choose the best settings. This kind of image optimization software is often called “Save for web”.

Color quantizer is a small program allows you to easily optimize images for web.

Optimize pictures without quality lossless.

A Mac app and Chrome extension that optimizes/compresses images and PDFs. Tinybeest also converts file formats and resizes images for the web.

Works with all common image formats like png, jpeg, bmp, tiff and Microsoft Office documents pptx, docx, xlsx.

Ximagic Quantizer provides 10 quantization methods: Uniform Popularity Octree Median Xiaolin Wu v2 Dennis Lee v3 Binary Split Lloyd (K-Means) NeuQuant SColorQ