This is a Brush Preset file for ZBrush. It is a chain brush.
If you don't own ZBrush, there is a tileable Chain link in the "Blend Files.zip"
These are optional utility textures baked from the high polygon models. They will come in handy should you plan to re-texture any of the models.
Can also be used when tweaking shaders.
This is a ZBrush Tool file. It contains all the high polygon source models.
For those that don't own ZBrush, there are OBJ versions of all the models in the pack.