There is not a clear line between for-profit and nonprofit organizations when it comes to accomplishing social good. There is, instead, a gradation of business structures to choose from.
Jim Fruchterman, a seasoned social entrepreneur, in his article "For Love or Lucre" (Stanford Social Innovation Review, Spring 2011) says, "I am structure agnostic: I believe that for-profit and nonprofit structures can both be good vehicles for improving society. You should look seriously at both as part of your toolkit as you're creating your new social venture."
Fruchterman says that what structure you decide to use will depend on your motivation, your market, your capital requirements, and how much control you wish to have.
Wherever you come down on those issues, here are the current structural forms that Fruchterman says can be used for social good.