RON

This paper describes an overlay network that is designed to improve recovery time in routing when failure happens and integrate path selection and routing more tightly with distributed applications. They argue that BGP infrastructure takes too long to stabilize.
Ron addresses this by forming a relatively small scale overlay network and maintain link state information to other Ron nodes. It actively sends out probes periodically to detect outage relatively quickly.

I like this paper because it gives a clear goal of overlay networks. It is usually designed to solve a particular issue that is difficult to solve without overhauling entire routing protocol. (in this case, BGP) However, just by limiting the scale of the problem and implementing functionality at application level, RON provides a practical path to deploy such systems. I think that is generally a big win for overlay networks and that's why they have been such active research areas.