Nektony's (http://nektony.com/) Duplicate Expert 2.0 is a useful cleanup utility for Mac OS X. It was developed specifically to help anyone find and delete all duplicate content, including hidden files as well as inspect duplicate files and folder - even similar folders.

Duplicates Expert can scan as many folders and drive as you select and do so simultaneously. The app collects files together as well as their characteristics.
Files are categorized by types and various folder types. Every category represents a joined duplicate cluster and file preview.

It's easy to remove all duplicate content using Duplicate Expert's features. Simply drag and drop multiple folders or drives and scan them for duplicate content. After a few minutes you'll get results allowing you to explore files by subcategory, and even follow the app's suggestions and hints.

You can change your reports by altering minimum duplicates' size, using the skip lists for specific files, folders, extensions and more. You can also specify autoselect options or choose an option to remove whole similar folders instead of folders' files one by one.

Duplicates Expert requires Mac OS X 10.9 or later and costs US$1.99. It's available at the Mac App Store.