A simple Blender add-on that shows what files (and what data from those files) is being linked into the current blend file.
(This screenshot will probably get outdated pretty quick, but you get the idea)
- After installing the add-on, you'll see a panel in the Scene settings.
- This panel automatically detects what files are being linked into this file and lists them. For each file, it shows how many of each kind of data-block there is.
- Click the little arrow on the left of each library to expand a full list of data-blocks.