[rdtennent]

Jamulus software is not only free (gratis and libre) but its use is completely anonymous: you may have to open a port but you don't have to open your inbox to spam or register in any way. And users don't need to authenticate to use a server, either "public" (i.e., advertised automatically in connection windows) or private (i.e., using an IP address known only to musical peers). There's no encryption but if you use a private server there's virtually no possibility of anyone other than designated peers to listen in.