It is hard to find a specific tool for writers and editors, but browsing in GetApp.com I managed to find a tool that looks like what you need.
Agilewords lets you share business documents, invite colleagues and clients to collaborate, schedule reviews and track all the changes. You can sign up for a 14-day trial on their website and check if this is really what you need.

You can also use applications that allow you to collaborate in text documents like Google Docs or a feature from Teamlab.

Google Docs is the easiest and most familiar solultion you will find. The writing/editing interface is almost exactly the same as Microsoft Word, so the user adoption is seamless. You can edit a document simultaneously with other members of your team, updates are automatically saved (so you never lose your progress), and it is simple to download to Word to share with more traditional users (if necessary).