Gnutella is a widely used peer-to peer network system for sharing all kinds of files, including music files. Each online Gnutella user or node can act both as a client by requesting specific files and as a server by providing access to files to be copied. Unlike the Napster model which has centralized servers, the Gnutella model has thousands of independent servers. Even though Gnutella is often used to provide access to copyrighted music just as Napster did, it is not considered to be a likely target for legal action.
To learn more about how Gnutella works, click the link below and view the animation How Gnutella Works.