File Juicer

File Juicer for Mac OS X

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ZIP, GZ, BZ2, SIT, SITX, HQX, RAR and other Compressed Files

File Juicer can find ZIP and RAR compressed files inside other files, mostly EXE files, but also from Java applications.
In the same way File Juicer can also find CAB and RAR files inside EXE files.

File Juicer does not unpack zip, tar, gz, bz2, sit, sitx, hqx, rar or bin files, as you can do this from Finder (at least on Tiger) or with Stuffit Expander or RAR Expander.

BOMArchiveHelper - extracts zip, bz2, tar and pax files

In Tiger you can use BOMArchiveHelper. You find it in System>Library>CoreServices but normally you can just double-click the file in Finder. Pax'ed files need to be dropped by hand, but they are usually also gzipped and then you can double click it.

The programs in CoreServices are not meant to be used directly, but they serve as helpers for other applications. You also find the Finder, and the Dock here, but they are normally (re)started automatically.