• etherpad / google docs / etherpad-lite
  • http://etherpad.org/
  • https://github.com/whackpad/whackpad (forked from hackpad (aquired by dropbox) which was in turn based on etherpad (aquired by google). more modern UI/UX focus than etherpad.)
  • https://firepad.io/#1 (requires hosted db)
• http://socrates.io/ (free as in “running on someone else's computer”)
• ckeditor → https://ckeditor.com/collaborative-editing/collaboration-features/

(merge from collaborative design at some point…)