Etherpad is an Open Source online editor providing collaborative editing in really real-time powered by Node.js
Mendeley announced the launch of a new “what-you-see-is-what-you-get” (WYSIWYG) citation style editor that will enable users to format citation styles and then contribute them to an open repository where they can be reused by other academics.
Produced in collaboration with Columbia University Libraries with the support of a grant from the Alfred P. Sloan Foundation, the new editor was developed in response to frequent requests on Mendeley’s user feedback board.
Source :Mendeley website
More details: here