The CC-by-sa open content license is the closest equivalent to the GFDL. Much GFDL corpus content is dual-licensed under CC-by-sa, sometimes with some clause specifying that attribution of collective work must include the most prominent five authors as per GFDL, and that Invariant Sections are either not allowed or restricted to the declaration of dual licensing.

Both are Share Alike licenses, so improvements must be available to all who might express any interest in them - and cannot be hidden from view, e.g. by ad hominem revert or (worse) ad hominem delete, which are not expressions of judgement of improved status of content, but instead, express a disapproval of a person or faction.

Wikitravel uses CC-by-sa, while some other services like Metaweb and Disinfopedia permit it as an alternative to GFDL, as long as the license is marked clearly in the initial description, notes, or text itself.

In LivingPlatform.CA, any content that is originally GFDL and contributed by its original author, or that is dual-licensed, or that is CC-by-sa and contributed by its original author, remains dual-licensed under both and is not subject to the non-commercial use only limits of the CC-by-nc-sa. It may be redistributed for profit as both GFDL and CC-by-sa allow, assuming that the most restrictive requirements of both are fully satisfied.