Moodle

Moodle is a 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 40,000-student University. This site itself is created using Moodle, so for a quick demo look at Moodle Features courses or these other Demonstration Courses. Moodle has a large and diverse user community with over 15,000 installations speaking 70 languages in 150 countries.