Software w/ Source for Sale?

frambooz asks: "As the GNU public license (amongst others) describes, you can make software that is free (as in freedom), but you don't have to make it *free* (as in free beer). I'm wondering if industry officials are aware of this fact, however. Do you know of any software packages that are Open Source, but still require you to purchase them? Did you ever work on such a project as a programmer yourself? If so, how did the development differ from a free(dom)/free(beer) Open Source application?"