RAR

RAR is a compression program offering an original algorithm. This new way to compress files provides greater efficiency, and makes smaller archives -- especially on multimedia files, and archives with many files.

RAR also offers self-extracting capabilities as well as disk-spanning (or multi-volumes). RAR is the official RAR archive utility for Mac OS X (offered as a command line utility), especially useful while reading all those alt.binaries newsgroups.
To use the RAR command line application, place the files in any folder on your hard drive, and call the utility by typing in the full path to the application (e.g., to run from the current directory, type "./rar" or "./unrar" followed by the appropriate parameters). Typing the application name (rar or unrar) without any parameters will produce a helpful guide to each program's usage.