The single-player Campaign assets for The Forgotten, packed into two optional files.
Unzip this file to the same folder as the one you installed The Forgotten Core and Music into.
This file is intended to be optional; The Forgotten mod should work just fine without it. If you're not interested in playing The Forgotten's campaign mode, then you can simply skip it and everything should work (except for the campaign, obviously).
The Forgotten's campaign requires both this file and the Music file to fully function. Without the Music file, no music will play on The Forgotten's campaign maps or screens.