Duolingo is a popular free service that offers activities for learning Spanish, English, French, Italian, Irish, Dutch, Danish, German, and Portuguese. The service works in your web browser and is available as an app on Android, iPad, and Windows 8.

Source: http://www.freetech4teachers.com/2015/08/how-to-create-classroom-in-duolingo-for.html#.VcsKZfmqqko