Moodle is a wildly, wildly popular LMS, and for obvious reasons. Offering the largest set of diverse features compared to other very task oriented and niche designs, Moodle brings an easily customized and diverse learning experience that allows the viewing of training in a whole new light. But, one of the big sellers of this LMS over other pretty equally competent solutions is the availability of Moodle plugins.
Moodle being open source, and with this readily developed plugin base as well, kind of pulls a Salesforce and offers theoretically boundless features. While there isn’t quite the slick App Exchange sort of channel here, Moodle plugins are quite extensive.