For the past year or so, there have been periodic questions raised about Drupal's licensing status. Is it GPL version 2? Are we moving to GPL version 3? Could we even if we wanted to? Is it OK to write a module that does [something weird]? As a member of the Drupal Association Board of Directors, I made it my task to sort out the answers to those questions.
Understanding licensing, and the differences between licenses, is more important than some realize. Open source is not the same as public domain. Open source and Free Software requires that source code be made available and that others are allowed to make use and share of the source code, but there are rules attached to how they can do so just as there is with proprietary software. For example, not all open source software can be combined, and there are requirements for how you distribute the source code of a program. Knowing which of those rules apply to Drupal, and to Drupal modules and themes, is important not only for the health of the code base (so we know what we can and can't do with the work of over a thousand people) but also to the health of the growing commercial Drupal economy.
I am pleased to announce that we now do have firm answers to these questions, and have a new and shiny FAQ up to answer them. There is nothing new in the FAQ; it is just a clarification of some edge cases that didn't used to exist.
We'd like to thank James Vasile of the Software Freedom Law Center for his help in working out the details. We also wanted to take a few moments to go into some of the reasoning behind how we reached a few of these conclusions.