Casual App for N3+

I’ve been learning Japanese for a few years. Mostly I learn via online a tutor and an hour a week conversation with a friend. Kanji/Grammar-wise I’d guess I’m about N3ish, but since I’ve mostly learned by talking to people I’ve no idea!

To supplement books, lessons etc I’ve been doing Duolingo as a way of getting a bit of learning/practice in on the go, when I’m waiting in line etc. Are there other apps that could also be useful to fill little 10 minute slots? Maybe better at teaching intermediate+ grammar than the green owl is?

Thanks!