for lower barriers to the use of a common codebase. The GPL camp, conversely, focuses on the perspective of downstream users , emphasizing that GPL'd code can't (easily) become the basis of a locked-down, unmodifiable, or (especially) incompatible system, accepting the costs of developers who choose to route around the GPL via reimplementation in exchange for higher barriers for those who want to lock their customers in. A couple of quick comments (even though I said I was done with this stuff).... Hopefully this won't be interpreted as more patting myself on the back... The most important part of "copyleft" is the "left" part, and it is frequently supported by folks that, implicitly or explicitly question the value of business and/or property. The GPL scares businesses. @Bob "Copyright was invented when reproducing something like a book or sheet music required capital equipment and setup time." Actually, it started as a tool for political censorship. But this whole if I write a book it is my property is part of a reification fallacy. Look at the picture of Margitte Ceci n'est pas une pipe . If you write a book, it is yours. But if you buy a book, it is never written by the author. It is printed in a shop by people who did not contribute to the formulation of the text. The object you buy was not created by the author. The author only supplied the arrangement of the characters in the text part. Every physical part of