Duolingo is a free website/application for language learning. The idea of the creator of the site to make the website free was very creative. While the users are learning, they help doing translations and Duolingo customers pay for the service.
I joined the website in July 2012, when it was not yet as developed as today, and I ended up forgetting the method after a couple of weeks. I only used it again in mid-2013 when I downloaded the app on my phone. Since then, I began studying with some regularity with it until I completed the French “tree”.