rockgod100

This plugin creates an area for site admins to jot down post ideas or assign post topics to content authors. Additionally, authors can be given due dates and suggested post types (article, video, etc).
Admins can also e-mail authors directly through the interface using an extension of the wp_mail() function.

Topic Manger

A quick way to remember post topics for single or multi-author blogs

Maxaud

This plugin adds a menu item to the admin bar that reads “Collaborate” that when clicked launches a TogetherJS instance.
There are various settings that allow you to configure the TogetherJS options to your liking.
Let me know what you would like to see in future versions.
What other functionality should be implemented to help you collaborate with others?

Collaboration

A collaboration tool to integrate TogetherJS in to WordPress.

Topic Manger vs Collaboration