R-Name is a free batch file renaming utility. You simply drag 'n drop files (or folders) onto R-Name and they are automatically renamed based on your settings. You can even preview the changes before actually renaming the files. The source code is available.
This app is one of the most useful I ever see :) I dread the moment it won't work anyway ... So many thanks to the author !
I've been using it for over a decade. I like this simple app that does the job.