The BP Group Documents plugin does something very simple and helpful: let’s group members share documents with each other.
When building social networks for people who are planning events or doing group assignments and projects, having the ability to share documents is essential.
This plugin gives you a page in each group where users can upload files. Since it ties in with the BuddyPress activity stream you automatically get notices and notifications when comments are made or new documents are added to your groups.
WordPress Educator Zac Gordon 