BetterZip is a utility I might not use every day, but I'm very thankful for it when I need it. It's an archive/compression utility which handles a broad array of archive formats, including ZIP, TAR, GZip, BZip2, and some that you rarely see on a Mac, such as 7-Zip and RAR formats. While the unarchiver built in to OS X can handle quite a few of these formats -- and is what I use on a day-to-day basis -- BetterZip adds a few very useful tools to the mix.
BetterZip opens or creates your archive in a file-list format, and you can drag files between Finder and BetterZip to add to or extract from the archive. Creating new archives is just a "File->New" or Command-N away, and you can save them in Zip, TAR, TGZ, TBZ, 7-Zip or XAR formats. While the Finder lets you easily create archives by right-clicking a file selection and choosing "Archive," it doesn't allow you to easily edit the archive or add to it. For quick compression of one or more files for emailing, it's fine and I use it regularly, but for larger archives that need to be more flexible, BetterZip is an excellent choice. BetterZip also makes it easy to search large archives for a single file you're looking for. Read on for more reasons BetterZip is my Friday Favorite ...
While there are free, dedicated utilities for unarchiving things like 7-Zip and RAR formats, it's nice to have one tool to rule them all. BetterZip handles multi-part RAR files with finesse. I don't deal with a lot of files in these formats, but on the occasion that I do, being able to display the full contents of the split archive and pick and choose what to extract is a useful trick.
Another area where BetterZip shines is with problematic archives. Have you ever had a zip file that wouldn't unarchive when you double-clicked it, instead throwing an error about permissions or some less-descriptive number? BetterZip rarely fails me on those occasions, I just do an "Open with" on the file, load it up in BetterZip, and the problem is solved. I can drag a selected file out or unarchive the whole thing to disk. One of the causes of errors I sometimes get is the archive being password-protected. OS X doesn't tell me this, it tends to just fail when it tries to unarchive the file. BetterZip has the common decency to offer me a password dialog.
BetterZip is US$19.95, with a free trial available at the developer's site. A competitor, Springy, can do many of the same things for the same price, but I prefer BetterZip's layout and aesthetic. If you're in the mood for a side-by-side comparison, Springy has a free trial available as well. If you just want to unarchive various formats not supported natively by OS X, The Unarchiver is a free utility you should take a look at. I'll also mention sArchiver, a Java utility with similar functionality for $15. Again, the extra $5 is worth it to me for the more Mac-like experience provided by BetterZip. If compression and archiving are part of your everyday life, a utility like one of these can definitely be a lifesaver!