Mutualist.Org is a fabulous site with hundreds of links, articles and more on Mutualism.
Mutualism, as a variety of anarchism, goes back to P.J. Proudhon in France and Josiah Warren in the U.S. It favors, to the extent possible, an evolutionary approach to creating a new society. It emphasizes the importance of peaceful activity in building alternative social institutions within the existing society, and strengthening those institutions until they finally replace the existing statist system. As Paul Goodman put it, "A free society cannot be the substitution of a 'new order' for the old order; it is the extension of spheres of free action until they make up most of the social life."
[via Early Days of a Better Nation (Ken McLeod)