I think this will be interesting for your community.
There are hundreds of language learning apps and hundreds of reviews and comparisons. Actually most of the comparisons are about the same programs. Are the apps really helpful or this is only ad and marketing? Yes, and Yes.
I have been studying English using various methods and resources over five years. Language learning is not my greatest talent but I have achieved B2 level (from A2) using only my smartphone and PC. I found a set of features that really helps you study a foreign language. Some of them are crucial, others are just useful. Under the cut you will find a rating of the language learning apps that I composed by analyzing these features, As Objective As Possible.