Automattic

Daniel Bachhuber

Gary Jones

Mohammad Jangda

Assign multiple bylines to posts, pages, and custom post types via a search-as-you-type input box. Co-authored posts appear on a co-author’s archive page and in their feed. Co-authors may edit the posts they are associated with, and co-authors who are contributors may only edit posts if they have not been published (as is core behavior).
Add writers as bylines without creating WordPress user accounts. Simply <a href="https://github.com/Automattic/Co-Authors-Plus/wiki/Creating-and-editing-guest-authors" rel="nofollow ugc">create a guest author profile</a> for the writer and assign the byline as you normally would.
On the frontend, use the <a href="https://github.com/Automattic/Co-Authors-Plus/wiki/Template-tags" rel="nofollow ugc">Co-Authors Plus template tags</a> to list co-authors anywhere you’d normally list the author.
For more detailed documentation refer to <a href="https://github.com/Automattic/Co-Authors-Plus/wiki" rel="nofollow ugc">the GitHub Wiki for this plugin</a>.
Co-Authors Plus is an almost complete rewrite of the <a href="https://wordpress.org/plugins/co-authors/" rel="ugc">Co-Authors</a> plugin originally developed by Weston Ruter (2007). The original plugin was inspired by the ‘<a href="https://txfx.net/2005/08/16/new-plugin-multiple-authors/" rel="nofollow ugc">Multiple Authors</a>‘ plugin by Mark Jaquith (2005).

Co-Authors Plus

No support at all , also it doesn't work with wpml

No Support - Not compatible with WPML

Not working

Works!

I rarely ever give 1 star reviews, but developers who take over a plugin - making a breaking change that took a while to resolve - and then refuse to follow standard practice by providing a changelog (despite requests) for future updates, cannot be trusted.

Avoid at all costs.

Cannot trust developers

Assign multiple bylines to posts, pages, and custom post types with a search-as-you-type input box.

Gianluigi Filippelli

<a href="https://wordpress.org/plugins/co-authors-plus/" rel="ugc">Co-Authors Plus</a> is one of the most useful plugin for multiple authors blogs. This plugin add a widget to add users’ avatars to post also for guest authors and for posts with multiple authors. 
You can also add avatars with a shordcode [blog-post-coauthors]. 
The plugin add also a slider in order to show user’s profile. If you want change the style, you can modify blog-spoiler.css file in the plugin folder.

Co-Authors Widget

The plugin add a widget and a shortcode in order to show authors of an article. It is compatible with Co-Authors Plus.

Co-Authors Plus vs Co-Authors Widget