CheckDupli is a powerful duplicate finder, can search and display all the duplicate files in a folder and its subfolders. It detects files that have the same name, but it detects as well files that have "almost" the same name, differing with accents, blank, or some specific characters.
Some advanced options allow you to adjust the filter criteria, taking accents, spaces or specific strings into account. You can set up lists of excluded folders, files or extensions.

The duplicates are displayed in a tree-like structure (called the result-tree) allowing you to see the file details and compare the duplicates attributes : file size, dates... It is possible to manually delete the useless duplicates files from within the application, or to launch the relevant application if the extension has been registered in Windows.
Check Dupli can also show the duplicates that have the same length. A Regex option can filter the filenames according to your own Regex strings.

Important : This program first produce a result-tree of the supposed duplicates. To be sure the files are equal, you can select a group of 2 or more files in the result-tree and compare the content in the compare menu

The license of this software is Free Trial Software, the price is $27.50, you can free download and get a free trial.