A recent request on the Boston Mac User Group mail list sent me looking for an app that compares folders and seeks duplicate files across drives. Singlemizer: The Duplicate Finder by Konstantin Pavlikhin fits the bill.
This US$19.99 one-trick pony was updated in mid-December to version 4.4.2 for OS X 10.8 and later. I had used it a few times over the summer, but abandoned it. Most of my complaints with Singlemizer were resolved with the recent updates, which include the ability to designate which files are the originals, a Quick Look Preview function, sorting and filtering by a variety of factors. Now, I like the app much better. I did all my new tests in OS X 10.8.4. You can use Singlemizer for free, but it will not remove any duplicate files until you purchase the app.
How It Works
You choose the folders in which to search for duplicates by dragging the folders into the Singlemizer main window and click Scan.
Singlemizer instantaneously switches to the list window. How fast it locates duplicate files depends on the size of your drives or folders. The speed is impressive, though. You can scroll through your resulting duplicate file or folder list to show particular files and sort them by seven different categories, such as size, number of duplicates, or file name. Singlemizer searches for duplicates on any media connected to your Mac.
When an item is checked for deletion and you select Remove Checked, the items are highlighted in red and you then have two dialogs in which to change your mind. You just click the magnifier icon to see the location of the file in a Finder window. Files can be moved to another location or the Trash, instead of deleting them or replacing the file with an alias to the original. After you dismiss the dialog below, yet another appears in which you can still cancel your choice.
One minor complaint, shown in the dialog above, you cannot choose individual files to move. You either move the whole file list, alias it or delete it. When you delete the file it disappears -- it does not get deposited into the Trash unless you select Move to Trash, so make sure you really want to remove that particular file as you cannot recover it.
There are some oddities in the Algorithm tab of the preferences and a trip to the Singlemizer Help file provided nothing useful. In fact, the help file only deals with information on different versions and license keys. If the program is designed to be used by only techies, it's fine. I'm guessing the everyday Mac user may not know what is a package, resource fork, hardlink, descendant directories, or a sensible system file. An explanation of terms would be helpful.
A trip through Google yielded nothing useful on descendant directories. It probably means subdirectories, i.e. a folder inside another folder. I recommend you leave the Algorithm tab set to the defaults, unless you have a specific reason to change them. I think Singlemizer would benefit users more if it had a more complete help file.
I found some minor issues still worthy of correction, but overall I recommend Singlemizer, especially if you do not have a strict file organization system. One note: in the File menu, the Open in External Editor commands seems to tell the file to open up in the program in which it was created. That command isn't clear and needs a new name, such as, Open in Original App, or some such.
Good One-Trick Pony
I knew Singlemizer could really help me clean out space when I found over 2 GB of duplicate photos inside of dissimilarly-named folders on a full backup drive. The recovered space was welcome. It also located all those annoying duplicate music files that are created every time I install an iTunes update. I recovered a few gigabytes of space on multiple drives, because Singlemizer found a few 700+ MB files with slightly different version numbers that I had saved into multiple folders.