[superasn]

I don't know of a more useful app than Duolingo till date and This is just another feather in the cap.

The only thing i don't understand about it is how it makes money? Yes, i read somewhere that they use it to translate news sites and documents but I've been playing it for almost 300 days now (uninterrupted streak) and still my French proficiency is nowhere near to make a worthwhile translation like any professional. This one really boggles my mind because it looks like they have a huge team and invest a lot of time and resources and so must have a lot of expenses.

[dyukqu]

There were optional in-app purchases and they have introduced Duolingo Plus recently - which enables users to download lessons for offline learning & removes ads. It's Android only for now and the price is $10 month. [0]

[0] https://www.duolingo.com/comment/22202238/Introducing-Duolin...

[borispavlovic]

I've been learning French for years. After having finished the course on Duolingo you have no reason to come back to the application. Memrise, for example, offers numerous courses for French, other languages, and other areas of knowledge. The repetition algorithm is superb and the ability to add your own courses as community contribution is killing.

[Axsuul]

They offer English certification and now serve ads after each lesson