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

itcoderr

When it comes to Blogging and online publishing, WordPress CMS is the go-to choice for individuals and large multi-authors publications. While managing your website, It would be hard for you to maintain and manage multiple contributors working on the same article. “Post Co-Authors” Plugin will help you to add multiple authors within same post, which makes the Job lots easier for you to track.
Add writers as bylines without creating WordPress user accounts. Simply create a user profile for the writer and assign the byline as you normally would.

Post Co-Authors

Post Co-Authors plugin allows you to select more then one authors in any post or custom post type.

Topic Manger vs Post Co-Authors