When you ask someone what license they are using for their open source hardware project, you’re quite likely to hear the answer “Creative Commons.” And unfortunately, that doesn’t fully answer the question.
The reason is that there is not a single entity called the “Creative Commons license.” Rather, Creative Commons offers a number of different licenses that can apply some rights and protections to your work, including the CC-BY and CC-BY-SA licenses which reflect open source values closely. In the 2012 and 2013 surveys these licenses were, in fact, the most popular licenses used for open source hardware documentation. (Creative Commons licenses cannot be applied to the hardware itself.)