Versatile Encoder allows you to encode your own videos into good quality DivX files. The input can be a sequence of files (as generated by blender), a single file (if you want to recompress something), or a VCD (if you need to back up a movie). This piece of software tries to guess good defaults and to help the user in making choices.
WebPack is a shell script for automatically packing Web sites by shrinking them without affecting their functionality or appearance. It is also useful for losslessly shrinking image collections and locating corrupt files. It works by stripping unnecessary information and optimizing the compression of images, and by removing comments/whitespace from HTML, using readily-available tools.
pngcrush is an excellent batch-mode compression utility for PNG images. Depending on the application that created the original PNGs, it can improve the file size anywhere from a few percent to 40% or more (completely losslessly). The utility also allows specified PNG chunks (e.g. text comments) to be inserted or deleted, and it can fix incorrect gamma info written by Photoshop 5.0 as well as the erroneous iCCP chunk written by Photoshop 5.5.