Napster is a protocol for sharing files between users. With Napster, the files stay on the client machine, never passing through the server. The server provides the ability to search for particular files and initiate a direct transfer between the clients. In addition, chat forums similar to IRC are available. OpenNap extends the Napster protocol to allow sharing of any media type, and the ability to link servers together.
opennap is a server for connecting the clients together, and is not a client itself.