Moodle is a Learning Platform or course management system (CMS) - a free Open Source software package designed to help educators create effective online courses based on sound pedagogical principles. You can download and use it on any computer you have handy (including webhosts), yet it can scale from a single-teacher site to a 200,000-student University. Moodle has a large and diverse user community with over 100,000 sites registered worldwide speaking over 140 languages in every country there is.
The market share for Moodle decreased by 0.048 percentage points (from 0.079% to 0.031%) for all sites, more than any other segment during the same period of time.
HTTP headers can provide some of the best clues about a site's CMS. The values of set-cookie and x-powered-by headers are the most common and easiest to find.
Markup
If a CMS doesn't have meta tags, it will often have other uniquely identifiable html markup. This can range from unique html comments, ids or classes.
Javascript
Similar to identifiable html markup, a CMS will sometimes insert unique Javascript code into web pages.