Simon Wheatley

A plugin providing template tags to list all active (or inactive) authors in the WordPress installation.
<pre><code><?php list_active_authors( 'days=30&include_protected_posts=0' ); ?> Will list all the authors active in the last 30 days, not counting password protected posts as "activity". Both parameters are optional.

<?php list_inactive_authors( 'days=30&include_protected_posts=0' ); ?> Will list all the authors NOT active in the last 30 days, counting password protected posts as "activity". Again, both parameters are optional.
</code></pre>
If “days” are not provided the tags default to the last 30 days. 
If “include_protected_posts” is not specified, the tags default to not including password protected posts.
The HTML output is fairly heavily classed, but if you need to adapt it you can. Create a directory in your theme called “view”, and a directory within that one called “author-listings”. Then copy the template files <code>view/author-listings/active-authors-list.php</code> and/or <code>view/author-listings/inactive-authors-list.php</code> from the plugin directory into your theme directory and amend as you need. If these files exist in these directories in your theme they will override the ones in the plugin directory. This is good because it means that when you update the plugin you can simply overwrite the old plugin directory as you haven’t changed any files in it. All hail <a href="http://urbangiraffe.com/" rel="nofollow ugc">John Godley</a> for the code which allows this magic to happen. Can hook into the <a href="https://wordpress.org/extend/plugins/user-photo/" rel="ugc">User Photo plugin</a> to display the author photos.
Plugin initially produced on behalf of <a href="http://www.puffbox.com" rel="nofollow ugc">Puffbox</a>.
Is this plugin lacking a feature you want? I’m happy to accept offers of feature sponsorship: <a href="http://www.simonwheatley.co.uk/contact-me/" rel="nofollow ugc">contact me</a> and we can discuss your ideas.
Any issues: <a href="http://www.simonwheatley.co.uk/contact-me/" rel="nofollow ugc">contact me</a>.

Author Listing

Allows listing of authors who are active or inactive within a defined recent period of time.

flocsy

Authors Widget shows the list or cloud of the authors, with the number of posts, link to RSS feed next to their name, avatar. It is useful in a multi-author blog, where you want to have the list in the sidemenu. 
The widget can also display an “Author Cloud” if <a href="https://wordpress.org/extend/plugins/seo-tag-cloud/" rel="ugc">SEO Tag Cloud plugin</a> is installed.

Authors Widget

Authors Widget shows the list or cloud of the authors in the sidemenu.

Author Listing vs Authors Widget