Moodle is a free and popular open-source learning management system that provides core functions for online courses like assignment submission, discussion forums, file downloads, grading, quizzes and announcements. It has been used for over ten years and can handle large class sizes. Moodle's main advantage is that it includes all the basic and advanced elements needed to run an online course and is highly customizable. The Moodle community is also very active in answering questions to help users.