List Compare takes two lists, one line per item, and works out the set relationships: the items in both, the items only in the first, the items only in the second, and the union.
Results are de-duplicated, and you can fold case or ignore surrounding whitespace. It runs in your browser.
Yes. Each result list shows each distinct item once, and the counts report both the raw and the unique sizes.
Everything that is in one list but not the other, which is the two only-in panels combined.
No, but results follow the order of the first list, then the second.
No. The tool runs entirely on this page.