GNU-FDL compatability
From the FDL website, this is the basic information regarding the compatibility between FDL and Creative Commons
Q. What is the rationale behind these changes?
A. Section 11 has been added to allow wikis like Wikipedia to use FDL-covered works under the terms of CC-BY-SA 3.0 if they choose to do so. They have told us that they would like to explore this option, and adding this provision gives them a clear path to do so.
Normally, these sorts of licensing decisions can and should be handled by the copyright holder(s) of a particular work. However, because Wikipedia has many copyright holders, the project needed some alternative way to accomplish this, and we've worked with them to provide that.
The other changes are minor improvements that were easy to make while we were at it. They've met with wide approval in GPLv3, and they don't change the license's fundamental permissions or requirements at all.
Q. Exactly what material can be licensed under CC-BY-SA 3.0?
A. In order to license an FDL-covered work under CC-BY-SA 3.0, a few conditions must be met.
The work must be available under the terms of FDL 1.3, which provides you with this permission. If the work was released under the terms of “the GNU Free Documentation License, version 1.2 or (at your option) any later version,” then it meets this criteria.
The work must not have any “Cover Texts” or “Invariant Sections.” These are optional features in all versions of the FDL.
If the work was originally published somewhere other than a public wiki, it must have been added to a wiki (or some other kind of web site where the general public could review and edit the materials) before November 1, 2008.
All FDL-covered material added to Wikipedia before November 1, 2008 satisfies these conditions.