Minuimus is a file optimizer utility script: You point it at a file, and it makes the file smaller without compromising the file contents.

Phatch is an user friendly, cross-platform Photo Batch Processor and Exif Renamer with a nice graphical user interface. Phatch handles all popular image formats and can duplicate (sub)folder hierarchies.

ShortPixel is arguably the top WordPress image optimization plugin: simple to set up, it can automatically optimize both your old and new images, as well as PDF files.

C++ file optimizer. It supports PNG, JPEG, GZIP, and ZIP files.

From developers to developers: a cross-platform tool for losslessly image compression.

Gifsicle manipulates GIF image files. Depending on command line options, it can merge several GIFs into a GIF animation; explode an animation into its component frames; change individual frames in an animation; turn interlacing on and off; add transparency; add delays...

Utilities for archiving photos for saving to long term storage or serving over the web. The goals are: use a common, well supported format (JPEG), minimize storage space and cost, identify duplicates / similar photos.

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...

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.

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.

tinyPNG.App provides a GUI front end for tinyPNG for your local computer so you can optimize images using the tinyPNG API service. Available on Windows, macOS & Linux.

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.