Patrick Robrecht

Posts and Users Stats offers statistics about the content and the users of a WordPress installation:
<ul>
<li>Posts per Publication Date</li>
<li>Posts per Taxonomies, i. e. per category, per tag and per custom taxonomies</li>
<li>Posts per Author and Post Type</li>
<li>Posts per Status</li>
<li>Comments per Date</li>
<li>Comments per Author</li>
<li>Comments per Status</li>
<li>Users per Role</li>
<li>Users over Time</li>
</ul>
All statistics are available as a diagram and as a table (which can be exported as CSV).
After the installation you can find the statistics as subpages of Tools.

Posts and Users Stats

Statistics about the number of posts and users, provided as diagrams, tables and csv export.

Chris A. a11n

This plugin requires PHP 5.3 or later, please check with your web host if you’re unsure.
Adoption uses the timezone that is set in the WordPres admin panel. Ensure you have set your local timezone in Settings > General.
Features:
<ul>
<li>Displays a bar chart with registration statistics for predetermined time periods (e.g. this week, last week, last 3 months, last 12 months, etc.)</li>
<li>Displays a “Quick Statistics” section which includes a summary of user registrations for popular time periods.</li>
<li>Easy to use, tidy and fits in with the overall WordPress user interface.</li>
</ul>

Adoption

Adoption displays user registration statistics in a neat dashboard widget

Posts and Users Stats vs Adoption