Discourse graphs are an information model for bodies of knowledge that emphasize discourse moves (such as questions, claims, and evidence), and relations (such as support or opposition), rather than papers or sources as the main units.
To give an intuition for what it is, here is a figure of a visual representation of a simple discourse graph for a body of literature on bans and antisocial behavior in online forums. You may recognize similarities to things like argument maps.
Consider how that information model foregrounds the conceptual building blocks and relationships that are important for synthesis, compared to a typical "iTunes for papers" model that foregrounds documents in a way that forces us to drudge through tedious extraction work before we can do the thinking we want to do!
This information model (theoretically!) has high potential for augmenting individual and collective "research-grade" synthesis (e.g., lit reviews for a dissertation or grant proposal).