I don't want to make it sound like I don't like Blackboard, but I can say that there are a lot of alternatives out there, and this one is free and is full of an active user-base so it is constantly improving and updating. It is "open source" so that means that anyone can design an "add-on" (aka, "app" or tool) to use with Moodle. I came across Moodle while I was doing research for a project on transformative learning. Moodle is designed to support a social constructivist approach to education.
Moodle is an acronym for Modular Object-Oriented Dynamic Learning Environment. The creator defines it as an online learning management system, designed to create opportunities for rich interaction between teachers and learners. The creator also uses it as a verb: the process of enjoyable tinkering that often leads to growing knowledge, insight, and creativity.
What can you do with it? I found this fantastic link that gives a quick overview (you can click through it in about a minute!) that uses Lego bricks. I can't think of a better way to explain it myself, so here's the link: http://www.slideshare.net/moodlefan/what-is-moodle-explained-with-lego-presentation. (Also, note the use of the page Slideshare.net, which I blogged about a few days ago, here.)
Here is a link to their Frequently Asked Questions: http://docs.moodle.org/24/en/About_Moodle_FAQ.
Have fun moodle-ing! :)
P.S., many of its features are free!