Bruce has a lot of data on a bunch of hard drives and he's looking for a way to catalog or collate the data, getting rid of duplicate files. Leo says there are de-duping tools that are designed to analyze and get rid of duplicates, but he'll run a risk of deleting something that only looks like a duplicate.
Gemini 2 is a popular duplicate file finder because it's intelligent and looks at the metadata of the file and even the file itself to hash out the duplicates. He should make sure that he's backed up before he runs it though, just in case. Fortunately, Gemini doesn't delete the files completely, they just move them to the trash. He should leave them there unless he needs to make space. Again, just in case. ChronoSync is a good way to keep his files synced and prevent dupes.