I would like to point out that NGOs using Plone (5) might be interested in a collaborative editing solution using
the Smashdocs editor.
The integration with Plone 5 is provided by myself for free as open-source.
Smashdocs itself offers free access to Smashdocs for elegible NGOs.
Find all details in my blog post
The integration of Smashdocs with Plone 5 is now available for testing on our Plone Demo site: www.plone-demo.info.
There is also a screencast on plone-smashdocs.zopyx.com showing how to do collaborative editing with Plone 5 and Smashdocs.
Yes, Smashdocs is a commercial component but there are almost no other comparable solutions on the market.