Duolingo - An excellent example of eLearning and gamification

I've been using Duolingo to study Spanish. The format makes a lot of sense to me and is an excellent example of using gamification principles in eLearning. Take a look at the article from the eLearning Mind website:
http://elearningmind.com/now-youre-speaking-language-duolingo-teaches-us-microlearning/

I appreciate the degree of user control, easily managed modules, multiple means of interaction, user reinforcement and the opportunity to ask questions/engage in social learning with other students.

If you haven't seen Duolingo, (http://www.duolingo.com) it's very much worth a visit.
And to top it off, it's free!