Mediawiki's visual editor has a (unreleased) collaborative mode: https://www.mediawiki.org/wiki/VisualEditor/Real-time_collaboration https://www.mediawiki.org/w

Mediawiki's visual editor has a (unreleased) collaborative mode: https://www.mediawiki.org/wiki/VisualEditor/Real-time_collaboration https://www.mediawiki.org/wiki/VisualEditor/Real-time_collab... Hits all those open-source client and server notes, and has the advantage of supporting everything that mediawiki does.