There are quite a few attempts at writing plugins that provide analytics data. Administrators have to be careful because many of these rely on other (often paid) external services, and other plugins arrive with a fanfare, but are not then maintained. This Analytics graphs Block started life in 2012, and has been continually upgraded through to Moodle 3.2.
The documentation link appears to direct to a page in Portuguese, and the Website URL is the GitHub page (with no additional documentation). I feel that if this plugin had better documentation, and a way of showing how dynamic and really useful the various reports are, it would likely be a lot more popular.
You can try this Block our for real on our public plugins site: http://plugins.moodlebites.com