Moodle is a free, open-source course management system (CMS).

A CMS, often referred to as a Virtual Learning Environment (VLE), is a web application which allows students who are registered on a course to access their course materials through a web browser.

It combines a lot of different features, such as file uploading, on-line chat, discussion forums, quizzes, surveys and so on.

There are many well known CMSs such as WebCT and Blackboard.

Moodle, however is different in that it is Open Source, which means that it is supported by a large community, continuously improving and extending its functionality.

It is also free to download and install on a server.

And very importantly, Moodle is a user-friendly learning-centered environment.

More information can be found at http://moodle.org/