Count user block
From Learnit docs
This plug-in is the block which counts the number assigned to the roll within a course like moodle1.9. Only an administrator can use. When it installs in the front page of moodle, this block considers the load of a server and a total button is not displayed.
You can be a registered user on the screen, such as moodle1.9 When you click the name of the role.
github: