pngquant!

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”.

FileOptimizer is a lossless file size optimizer supporting AIR, APK, APNG APPX, BMP, CBZ, DOCX, DLL, EPUB, EXE, GIF, GZ, ICO, JAR, JPEG, MNG, MP3, MPP, PNG, PPTX, ODT, OGG, OGV, PDF, PUB, SCR, SWF, TIF, VSD, WEBP, XAP, XLSX, and ZIP file formats among others.

Caesium Image Compressor lets you compress your pictures up to 90% without visible quality loss. Providing a simple yet effective interface with a real-time preview and multiple image processing at the same time, everyone will be able to reach the best result. Advanced users will find extra features, like metadata storing options or folder structure support.

-Combines PNGOUT, OptiPNG, and DeflOpt to create the smallest PNGs-No image quality is lost — only file size-Converts JPG, GIF, TIFF, and BMP files to PNG-Ultra-configurable

Phatch = Photo & Batch! Phatch is a simple to use cross-platform GUI Photo Batch Processor which handles all popular image formats and can duplicate (sub)folder hierarchies. Phatch can batch resize, rotate, rename, ... and more in minutes instead of hours or days if you do it manually. Phatch will also support a console version in the future to batch photos on web servers.

TinyPNG uses smart lossy compression techniques to reduce the file size of your PNG files. By selectively decreasing the number of colours in the image, fewer bytes are required to store the data. The effect is nearly invisible but it makes a very large difference in file size!

OptiPNG is a command-line 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.

JPEGmini is a patent-pending photo recompression technology, which significantly reduces the size of photographs without affecting their perceptual quality. The technology works in the domain of baseline JPEG, resulting in files that are fully compatible with any browser, photo software or device that support the standard JPEG format.

PngOptimizer compresses graphics files and removes extra, unnecessary data without affecting quality. It will update PNG files or converting BMP, GIF or TGA files to the PNG format using simple drag-and-drop. You can also paste a clipboard image straight into PngOptimizer and get a PNG file directly.

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.

With Image Optimizer you can losslessly optimize your PNG, JPEG and GIF files and thus save your bandwidth and your users' time! Kraken recompresses images with blazing speed and strips metadata with image quality intact.

TruePNG is one of the most advanced PNG optimizers available. It does the most exhaustive checks for reductions, that lets it to optimize further, even if it uses a less efficient compression algorithm than others tools.

optimus.io offers lossless compression of images available with a WordPress plugin and via API. Benefits: - The file size will be reduced but the image quality remains the same- Bulk optimization- Conversion also to WebP available