Lines can be drawn: - Public domain. This is completely open. - Free to use and modify and sell but must retain author's name internally. (BSD-ware) - Optional clause: Must not advertise that it contains content made by the author. (Since the author didn't oversee the modifications, the author isn't associated with the final product.) - Free to use and modify and sell but must redistribute the original material. (GNU-ware) GNU is not free; it is viral and infects anything it touches with it's own license restrictions. - Free to use for a limited time and share with others, but not modifiable. (Share-ware) - Free to use but not modifiable. (Free-ware) - Pay to use but not modifiable. (Commercial-ware) - Pay to use and extendable but not modifiable. (Commercial-ware with third-party plugins)