GFDL versus CC-by-sa
The GNU Free Documentation License (GFDL or GNU FDL) was made with the main purpose of being used for softare documentation. CC-by-sa is intended for general sharing of "cultural works". The differences are quite technical, and the key principles are identical. The main difference is:
- Attribution - any copy of a work licensed under the GFDL must include a full copy of the license. That's not a big burden in software, but if someone is printing off a GFDL document, they are legally obliged to include a license printout which may be as long as the document. The CC-by-sa is much simpler, requiring attribution as requested by the source, which typically is the source's name (e.g. "Practical Action," "Appropedia" or "Jodie Smith"), perhaps a title, and a link.
Some advantages of CC-by-sa are:
- CC's human readable versions do a fair job of representing the conditions of use, in much clearer terms. Compare the CC-by-sa (human readable version) with the GFDL.
- CC-by-sa has become the de facto license for web use, for those wanting similar conditions to the GFDL - used by Wikipedia and many other wikis, available as an option for Flickr and other content sharing sites. It's recognizable, and compatible with many other sites.
Note that the FSF, who manage the GFDL, did give permission during a certain window of time for wiki sites to relicense their content from GFDL to CC-by-sa. Wikipedia and Appropedia did this, among others. The FSF recognized that CC-by-sa gives a greater flexibility that is needed for wikis in particular (and some would say, for content sharing in general).
If you want to go with CC, there are other questions that would be considered, but it's probably overcomplicating things. But in the interests of thoroughness.
- Do you want to be even more open and use CC-by, without the "Share Alike" requirement? Possibly not, if you want to guarantee that you are able to incorporate modifications and additions by other people, when you want to; also, you can make that decision at any time later without affecting any of the CC-by-sa users of your content.
- Do you want to dual-license, letting people know they can use under the terms of either CC-by-sa or GFDL? Probably not, as it breaks your ability to use other people's work. I.e. If you want to incorporate a modification or addition done under only one license, you can't (in a strict legal sense) then take it and publish again under your dual license.
Comparison of GFDL and CC-BY-SA - an essay in Wikipedia's project space.
NOTE: This is an adaptation from an email (7 March 2012) and needs to be thoroughly fact-checked, and have unfair aspects removed. It's written from a pro CC-by-sa perspective and might be unfair to the GFDL.