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Advogato: Socializing the Web with trust metrics
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Key facts: Enables users to find collaborators based on social nets of mutual trust in a form of collaborative filtering. Software developers are only referred to people they trust to help them, and the people they trust, and so on. (Like Clairol.)

So what?: Advogato employs a "trust metric," which produces networks of trusted colleagues.

What is a trust metric?: Authentication using a path of trusted intermediaries, each able to authenticate the next in the path. It is a well-known technique for authenticating entities in a large-scale system. Recent work has extended this technique to include multiple paths (Reiter and Stubblebine). Advogato's basic trust metric evaluates a set of peer certificates, resulting in a set of accounts accepted. These certificates are represented as a graph, with each account as a node. The goal of the trust metric is to accept as many valid accounts as possible, while also reducing the impact of attackers (from Advogato.com).

May the force be with you: "Certification," Advogato's term for network reputation, covers three different levels: Apprentice, Journeyer, and Master.

What are these graphs, nodes, and directed edges?: I have no idea. It has something to do with identifying "good," "bad," and "confused" servers by virtue of the nodes, or accounts/users, on that server. In other words, good Advogato constituents lend credibility and reputation to the servers they use to participate on the site. "Bad" constituents do the opposite to their servers. If enough "bad" trafficks through a server, the server is prevented access to the participation/posting on the site. Spam, therefore, is (eventually) eliminated, as are bogus accounts/users.

Sources:
--Michael K. Reiter and Stuart G. Stubblebine (Bell Laboratories, Lucent Technologies), "Authentication Metric Analysis and Design," available at http://www.cs.columbia.edu/~stu/99TISSEC-metrics.pdf [accessed March 9, 2002].