This was something I used for SMF and was very useful to my user's. It's a basic function that shows recent attachments. That's all. For xenForo, there could be a link under "Forum" beside "What's New" that says "Media" or "Attachments". Click on that ink and it brings up a page showing recent attachments with file size and user. Of course, any images will be shown, not just a file. That's all there is too it.