GPL

licence of GNU Emacs.

GPL in a nutshell

• Someone A create a recipe of beer. and publish it as GPL
• here is what another guy B can do, have to do
  • B can make beer made with this recipe
  • B can make money by selling beer made with the recipe
  • B can improve the recipe, and publish it
  • B can tell the recipe to others
  • B can improve the recipe, but must publish it as GPL
  • when someone C ask B, what the original recipe, B have to tell him
  • when someone C ask B, what the improved recipe, B have to tell him
• in one sentence, when A create a recipe of beer, publish it as GPL, recipe and any improved recipe will be public accessable forever, and any one can make money by making and selling the beer