Duolingo is a free website and mobile app you can use to learn commonly-spoken languages, including ESL (English as a Second Language), in a game-like setting.
Challenge yourself to devote as little as five minutes a day learning your language, and earn badges for completing skill sets.
To save and track your progress, you will need to set up a personal account using an email address and a password you can remember.
There is also an educational version, Duolingo for Schools, that allows teachers to work with students in a group setting and track their progress online.
Right now, English speakers can choose from Spanish, French, German, Italian, Portuguese, Dutch, Swedish, Irish, Russian, Turkish, Danish, Norwegian, Polish, Esperanto, Ukrainian, Welsh, Vietnamese, Hebrew and Hungarian, with pending courses planned in Greek, Czech, Swahili, Romanian, Hindi, Indonesian and Korean.
Popularized by an app for iOS and Android, this service is free, and critically rated, and uses translations provided by users to help translate portions of Wikipedia and other open source websites into and from other languages.