ClusterFlunk is simply a tool that allows students to talk to the other students that are specifically in their classes. By talking they can instant message, upload/download files (study guides, lecture notes, past exams, etc), and post on their class walls. Email email@example.com for a product username/pass. (blocked by .edu).
Was successful at our beta, University of Iowa (10k+ users in two semesters), found a recipe to scale, and have scaled to 50 public universities around the nation in January 2014.