atool is a free and open source script built for managing file archives of various types (tar, tar+gzip, zip etc).
The main command is aunpack which extracts files from an archive. Did you ever extract files from an archive, not checking whether the files were located in a subdirectory or in the top directory of the archive, resulting in files scattered all over the place? aunpack overcomes this problem by first extracting to a new directory. If there was only a single file in the archive, that file is moved to the original directory. aunpack also prevents local files from being overwritten by mistake.
The other commands provided are apack (to create archives), als (to list files in archives), and acat (to extract files to standard out). As atool invokes external programs to handle the archives, not all commands may be supported for a certain type of archives.
atool identifies archives by their file extension. Sometimes this is not possible - for instance rar archives usually have varying numeric file extensions. In those cases when atool can't identify the format, file is used instead. (atool can be configured not to use file.)