Duplicate Lines Remover is a simple tool which can process text files and strings in various ways.
By default the program will work just as its name suggests, quickly processing files to remove duplicate lines.
Check the Settings menu, though, and you'll find options to ignore or remove empty lines, or to sort the lines in a file.
The program can also work with strings. Which means you can paste in text from the clipboard, process it to remove duplicates and so on, then copy it back to the clipboard.
And a command line version helps you automate the process, scanning files, processing them and saving the new versions without any further input required from yourself.
It really should be a portable application, but otherwise Duplicate Lines Remover is a simple and straightforward text processing tool