So, is Duolingo a program or a website? The one I downloaded was an app. The program we need to create ourselves, manage ourselves, motivate ourselves and get along with others ourselves. It's fun for inexperienced language learners. Highlight on fun.
A lot of the times, though, interacting on unsupervised language learning websites could discourage you, because some "learners" like to point out what's wrong and what's right. In my opinion, if you have your own language learning program and goals, it does matter a lot how you get there.
I tend to get confused when I learn unsupervised, so I would quickly design something, like a program or something to help me with the learning. Here in this Forbes
story, the founders of Duolingo are featured. Duolingo was just starting out in 2013. Hint: Rosetta Stone gets a mention.