Moodle is one, if not the most popular free/open source LMS platforms available. When it comes to LMSs I would argue that Moodle may have the best name recognition of any LMS in the industry. And for good reason—it’s free, relatively easy to install and host on a server, and has a wide variety of plugins, including a relationship with PayPal to make selling your course work using eCommerce easy.
You can download your own build of Moodle for free from the Moodle Project at www.moodle.org, or take it for a test drive by visiting www.moodle.com and logging in through various user roles. They even give you the ability to mess around with it and try to break it, with the site resetting every hour.
I am currently building out and evaluating Moodle. You can visit it here. You can log in as a guest to tool around and view some content that I have posted for public viewing.
With Moodle’s increasing popularity, web hosts are making it easier to install your own build. In fact the host that I use actually has a one-click-install for Moodle, making getting up and running as easy as choosing a domain or sub-domain, and literally installing with the click of a mouse.