CloneSpy

Works fine, does find duplicates, just probably not using it right. There is multiple search options, duplicates will look for same content (I think) whereas the better option for me was Files having the same name, as I had copied a folder and added some data to the new folder, so this found those duplicates.

It has a unique feature of custom pools where you can search for dups either inside one or between two of them.

worthless and doesn't find anything in a folder full of duplicates

Fast and reliable, with many detailed options.

You may also just unzip the installer with something like 7-zip to have a folder with the program in it.