When I was asked to review The Unarchiver 2.7, a free decompression utility from Dag Ågren/WAHa, I thought "Who needs this program, when Mac OS X opens most common archive formats?" I quickly found out that thousands of people rely on The Unarchiver to do tasks that lie beyond the scope of built-in Archive Utility.app found in OS X.
First I spoke to a loyal user, Barry Porter, an Apple Consultants Network member from Delray Beach, Fla. He said, "I use it everyday. It's great. I haven't found an archive it can't open. I use it because the built-in program is very limited in what it can create and open. You never need to open the program, it just works in the background unarchiving stuff." That's a glowing recommendation, so I put The Unarchiver to my own test.
Back in the old days, it was common practice to archive files by compressing them so that they fit on a floppy disk or CD. If you happen to have saved those files onto a hard drive socked away for safekeeping, today you are hard-pressed to open those files. The Unarchiver can decompress many file types, so rejoice, because you can actually open DiskDoubler, Compact Pro and PackIt files now.
I dug up some seriously old files to test The Unarchiver. I found some .sit files from 1994 and The Unarchiver opened them. Oh joy! Anyone need an Macintosh FTP list from 1995? (Curiously though, my search for files created before 1999 found over 1000 files created in 1969. I'm pretty sure that's not right! Must be a backup from a crashed drive... but I digress...)
If you use more current formats and various download sites, you may encounter RAR or Tar files. No problem for The Unarchiver there either. If you find bugs or have a problem, Dag Ågren maintains an old-school support board on which you can ask questions. Also included is support for over 29 languages and DOS and Windows formats.
To install, you only need to download it from the App Store. The program runs in the background. When you double-click on the application, all you see is the Preferences window.
The only time you have to interact with the program is to give it permission to write to a folder, if you want to extract an archive into the same folder in which it lives.
If you're curious and want to know exactly how many different archive formats exist, first look at The Unarchiver Supported formats page. Second, take a gander at Wikipedia's "List of archive formats." This handy page explains all of the file extensions used on various platforms for archived and compressed formats.
In short, if you need to open archives of any flavor, you can't go wrong installing The Unarchiver. If you like it, you can donate to help Dag Ågren's development efforts for other programs too.
OS X 10.6.0 or later