If you are ever in need of file or folder comparison on your computer, then you need BeyondCompare.  One use of BeyondCompare is to simple compare file directories that contain files with the same name, but with different file extensions.  For example I had directories of thousands of DICOM images (.dcm file extension). I ran a batch process on these images to create JPEG versions (.jpg file extension) of these same files.  The JPEG images had the same file name and directory structure.  The JPEG images were initially created in the same directories as the DICOM images and I actually used BeyondCompare to quickly move them out to their own directory.  But then I wanted to make sure all of my DICOM images had a JPEG counterpart.  I needed BeyondCompare for that as well.

In BeyondCompare 3, I aligned my DICOM (on the left) and JPEG image files (on the right) using the following session settings in the software:

Select Session > Session Settings.
Go to the Misc tab.
Click New.
For "Align left file (or folder)" enter "*.dcm".
For "with right file (or folder)" enter "*.jpg".
Click OK until you're back to the main window.

This will show you if there is a matching JPEG file name for each DICOM image.

BeyondCompare is an invaluable tool if you are a software developer, data manager, or data analyst.  Below is what the software looks like comparing folders: