Features

Moodle is an active and evolving product. This page lists just some of the many features it contains:

Overall design

Promotes a social constructionist pedagogy (collaboration, activities, critical reflection, etc)
Suitable for 100% online classes as well as supplementing face-to-face learning
Simple, lightweight, efficient, compatible, low-tech browser interface
Easy to install on almost any platform that supports PHP. Requires only one database (and can share it).
Full database abstraction supports all major brands of database (except for initial table definition)
Course listing shows descriptions for every course on the server, including accessibility to guests.
Courses can be categorised and searched - one Moodle site can support thousands of courses
Emphasis on strong security throughout. Forms are all checked, data validated, cookies encrypted etc
Most text entry areas (resources, forum postings etc) can be edited using an embedded WYSIWYG HTML editor

Site is managed by an admin user, defined during setup
Plug-in "themes" allow the admin to customise the site colours, fonts, layout etc to suit local needs
Plug-in activity modules can be added to existing Moodle installations
Plug-in language packs allow full localisation to any language. These can be edited using a built-in web-based editor. Currently there are language packs for over 60 languages.
The code is clearly-written PHP under a GPL license - easy to modify to suit your needs