Duolingo is the language learner's best friend. The app is a fun and fast way to study a new language or brush up on an old one through immersive game-like lessons, and its curriculum is surprisingly thorough. Currently, Duolingo supports 19 different languages and allows the user to set goals from five minutes of practice per day to 20. Continued practice allows you to unlock further lessons and getting to the next level becomes addictive. It is easily one of the most effective language-learning tools available, and the best part — it's totally free!