ownCloud Documents is described as 'is collaborative editing of rich-text documents that lets up to 5 individuals collaborate to edit .odt or .doc files securely within the browser' and is an app in the News & Books category. There are three alternatives to ownCloud Documents for a variety of platforms, including Self-Hosted solutions, Firebase, Cloudron, Windows and Linux. The best alternative is Etherpad, which is both free and Open Source. Other great apps like ownCloud Documents are Gobby (Free, Open Source) and Firepad (Free, Open Source).
Etherpad is a highly customizable Open Source online editor providing collaborative editing in really real-time. Collaborating in really real-time No more sending your stuff back and forth via email, just set up a pad, share the link and start collaborating!