I am working on a social media system of my own. For very small groups. This is a screenshot of the current build of Palimpsest, an annotation service for collaboratively editing documents. Unlike a Wiki, there is structure. Alice, Bob and PHB are editing an Internet Draft.

There is a style sheet but it is turned off for now to help isolate issues during debugging. The basic idea is that each comment on the draft creates a task which has its own lifecycle from open to cleared. So, these are mini-issues anchored to particular document paragraphs.