Moodle is a Free/Open Source LAMP type software application. It can be described by going to http://moodle.org/? and copying the stuff they say and pasting it here:
Moodle is a Course Management System (CMS), also known as a Learning Management System (LMS) or a Virtual Learning Environment (VLE). It is a Free web application that educators can use to create effective online learning sites.
One page links to Moodle:
lib/main.php:944: Notice: PageInfo: Cannot find action page