Moodle is a course management system (CMS) - a free, Open Source software package designed using sound pedagogical principles, to help educators create effective online learning communities. 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 University with 200,000 students. This site itself is created using Moodle, so check out the Moodle Demonstration Courses or read the latest Moodle Buzz.