Dupe Guru has been a useful GUI on windows. It is also cross platform.

https://dupeguru.voltaicideas.net/

If you seed from the same drive where you store your files, learn the art of hardlinking any torrents you’ve downloaded (that don’t require unpacking), and you can seed without taking up too much more space on your drive.

Hard links are essentially links that point to the same file. When one link is deleted, the other still exists and it is only when the last hard link is deleted that the underlying file is actually deleted.

For Windows see the following site for a hardlink tool that is integrated with the right click menu - https://schinagl.priv.at/nt/hardlinkshellext/linkshellextension.html