CC-by-sa

CC-by-sa is the standard abbreviation for the Creative Commons attribution sharealike license, closest equivalent to the GFDL. It is less specific than the GFDL regarding number of attributions required and Invariant Sections, which is one reason it is preferred by some projects, e.g. Wikitravel. Text liberation may be easier under GFDL however as many GFDL corpus access providers give up their rights by violating GFDL.