The Unarchiver is a much more capable replacement for "Archive Utility.app", the built-in archive unpacker program in OS X.
The Unarchiver is designed to handle many more formats than Archive Utility, and to better fit in with the design of the Finder. It can also handle filenames in foreign character sets, created with non-English versions of other operating systems. Supported file formats include Zip, Tar-GZip, Tar-BZip2, Rar, 7-zip, LhA, StuffIt and many other more or less obscure formats. It is localized into Japanese, German, Spanish, French, Portugese and Russian.