Mac OS X already has an Archive Utility app built in, but it’s a capabilities are rather lacking. It only supports extracting from ZIP (.zip), GZIP (.gz), and a number of other less popular formats. There are a few apps like UnRarX and RAR Expander, but my personal favorite is The Unarchiver.
The Unarchiver is an open source app. It works seamlessly within OS X just like the built-in Archive Utility but supports a wide range or archive formats, including RAR archives. You don’t need to launch any app to extract archives; simply doubling clicking on your archive, and The Unachiver does the rest.
Download The Unarchiver. Requires Mac OS X v10.3.9 or higher.
Another neat fact about The Unarchiver is that if you start extracting from an archive while it’s already working on a different archive, it will wait for the first one to complete before started the second task. This allows you to queue a set of extracting tasks quickly without slowing down your system. It may not be an intended feature, but this behavior is really useful because when more than one archive is being extracted, they take longer to complete than having them completed one by one. It’s considerably slower when multi-tasking, this is especially evident with magnetic hard drives and other storage mediums with moving parts and slow seek times.
Once you download The Unarchiver and drag it to your Applications folder, launch the app and you will see the Preferences window. From here you can select/deselect the archive format you want it to be associated with. Also, under the Extraction tab, you may select a default directory for output, or you may leave it to ask every time.