The System Information module displays information about the current state of the Drupal installation and system environment.
This module provides several overviews such as number of content and users, user roles and their permissions, installed modules and themes incl. version numbers, date stamp, filename, and more.
And also gives an overview of the current state of PHP and the database system.
And allows to browse through the database tables.
For more information and screenshots, see the handbook entry for System Information module.