Streamer is a beta p2p internet radio program. It allows small broadcasters to easily broadcast to many users by not requiring large amounts of bandwidth. The protocol was made from scratch to be as efficient as possible. Both windows and linux versions are availible. Streamer is free for non-commercial use.
According to the web site above - Streamer counts listeners and can report them by XML/HTTP. It's the only p2p streaming server that we know of that provides real-time Average Quarter Hour (AQH) tabulated ratings over the last 24 hours.