Posts and Users Stats offers statistics about the content and the users of a WordPress installation:

• Posts per Publication Date
• Posts per Taxonomies, i. e. per category, per tag and per custom taxonomies
• Posts per Author and Post Type
• Posts per Status
• Comments per Date
• Comments per Author
• Comments per Status
• Users per Role
• Users over Time

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.