I spent 10 minutes or so playing around with this and it is impressive. I've also built a couple of small side projects around language learning out of frustration with Duolingo.

I'm around a C1 level in French and am just starting to learn Polish. The audio pronunciations are a great feature here and (at least in French, where I can judge it) the accents are quite good. I can see this being quite useful for my Polish work for learning some of the basics.