Just added to MediaWiki.org: http://www.mediawiki.org/wiki/Extension:WorkingWiki

WorkingWiki is a software extension for MediaWiki that makes a wiki into a powerful environment for collaborating on publication-quality manuscripts and software projects. It's designed for research labs' wikis, but may have diverse other uses as well.

(I probably should have made it public long ago, but there was a big refactor and it took a long time to settle out...)

Lee Worden McMaster University