I want to publish a lot of documentation on programming and other similar topics I have been writing over the years.
The documentation consist of explanations, diagrams, exercises and code examples.
At this moment most of the content is my own, with some contributions from people who I personally know.
My requirements are:
The license must be free.
I would prefer a copyleft license.
I want to accept contributions from anyone, but I don't want to maintain a big file that explicitly states every contributor, unless the contributor herself adds her to the list.
I want to facilitate the integration of parts or the whole of these documentation to any other free project, no matter which license they are using.
What license would be the most appropriate given these requirements?
Note that I'm looking for a "soft" copyleft: I want to avoid helping private projects, but I don't want to restrict others licensing choices.