Over the past few years I have tried every language learning app I could find. The most success I have had is with LingoDeer. The formatting and I instructions really give that feeling of a classroom lesson. Learning Korean as an English speaker has been very challenging. I feel that LingoDeer has gotten me further in a few weeks compared to what I learned with a months of Duolingo or Rosetta. Duolingo if not paying for it becomes absolutely ad filled and frustrating.