Very rarely will I create a thread to praise an app but this hidden gem really deserves some attention.
The Unarchiver
This thing decompresses almost every format you've ever heard of (perhaps not all but most of them anyway

)
This app is perhaps your best companion if you have to deal with a lot of old archives for Mac OS emulation (vMac, BasiliskII, SheepShaver). It decompresses .sea, .dd, .bin, .hqx. Perhaps the only missing format in that list is the Compact Pro format .cpt. Ah well, still nice to see so many old formats supported by this app. If you deal with Amiga emulation, this app deals with pretty much every Amiga compression formats.
This app can extract Windows Self-Extracting Archives.
The list goes on:
zip,
gzips,
bzips,
7z,
rar,
tar.
Perhaps this app's crowning achievement is that it can extract Stuffit Archives. I had been looking for an app to replace Stuffit a few years ago but never found one. For the last two years or so, I have refused to install Stuffit onto my computer and systematically refused to use any app that was archived in the .sit format because I loathe Stuffit so much (the format is fine, the app and the company behind Stuffit are not)...I only recently found The Unarchiver but it seems like it's been around for a while. This app is worth it if only for it's Stuffit Archive support. It doesn't support .sitx but thankfully there aren't very many .sitx archives out there.
To top it off...this app is tiny (2.9MB if you remove the localizations and most of the size coming from the 128x128 icons associated with every format it can decompress) and everything is self-contained (unlike Stuffit which installs things like its decompression engine in your Library folder, ugh.)
You can also, following instructions on the author's site, replace Mac OS X's archive helper with this app. This is not necessary, however...simply keeping the app on your hard drive and check-marking the formats you want The Unarchiver to handle will allow The Unarchiver to decompress them.
It's an awesome app. This app should definitely be in the 'What application do I use if I need to...?' sticky. There's no reason why this hidden gem should remain hidden.
edit: I did a quick search in the forum and noticed that a few people actually already knew about The Unarchiver.

And they seem pleased with it. I really find that it's the unarchiver Swiss Army Knife. It does almost everything. If you're juggling a few apps to decompress formats such as rar, sit, and zip, you can almost do away with them and get The Unarchiver. Keep in mind, however, that this app only decompresses files. It does not compress files. If you're looking to compress to sit, rar, or zip, you'll need other apps. I strongly suggest to never use Stuffit to compress a file though.
