If you use it for sçhool, or a private course I can recomend QUIZLET. You can connect units from other users, or create your own. It’s a bit like a free Version of PHASE 6 (I only know the free Version of QUIZLET…)
But it’s totaly not like DUOLINGO.
- DUOLINGO is stand alone.
- QUIZLET is a helping tool for an existing course.
A “Bird of Prey” with 1500 pieces and legal license, in the blue week for 35 bucks will never be available again. Unfortunately, I found out about it too late.