I don't much of formal anything, but here's a list of some attempts by people to formalise the distribution of free music. I have reservations about many of these licenses because they tend to fight fire with fire (i.e., using copyright law to keep music free). Do the ends justify the means? I think that's up to an individual musician to decide. I make a statement about the unrestricted nature of the music I create, but it goes without saying.