Paste a list and the tool keeps the first occurrence of every line and drops later repeats, preserving the original order. Turn on "ignore case" to treat Apple and apple as the same line, and "trim spaces" so lines that only differ by leading or trailing spaces count as duplicates.
No. The first copy of each line stays where it was. To alphabetize as well, use the sort lines tool.
Yes, as long as there is one item per line. Everything runs in your browser, so nothing you paste is uploaded.
See also: sort lines alphabetically · word counter · case converter