Edit Flow is a free plugin you can easily download and install from the WordPress.org plugin directory.
For WordPress.com VIP clients, Edit Flow is available in the shared plugins repo and can be activated through your VIP dashboard.
Calendar - A convenient month-by-month look at your content.
Custom Statuses - Define the key stages to your workflow.
Editorial Comments - Threaded commenting in the admin for private discussion between writers and editors.
Editorial Metadata - Keep track of the important details.
Notifications - Receive timely updates on the content you're following.
Story Budget - View your upcoming content budget.
User Groups - Keep your users organized by department or function.