This page is actually harmless unless you get the original from me, set up your computer to act as a web server, and run it locally. PHP, being server side code, doesn't have access to your local files, and in any case, I've removed it from this online version. I don't want you able to try to mess with files on my server, after all!
Anyway, I don't know if most people bother to name their files, but I do, sometimes in groups, and so this has saved me a lot of time. A lot of boring, mindless-task time.
That being said, I think the following will give you a good idea what this tool can do...
WARNING: THERE IS NO UNDO FUNCTION!!!
ALWAYS make a backup of target folder, always.
I can't foresee every situation, and crap happens. With programming like this, a metric ton of crap can happen, and happen very fast. It's quite possible for the new name of one file to be the same as the new name of another, but there is no rejection here, nor confirmation of your desire to delete a file, as there is when renaming files in File Explorer.
NOTE: the Replace and Remove options accepts regex patterns. Rename cannot make use of regex, as it doesn't look at what the existing file names are.