Not your typical Russian grammar app
At the time of writing I have 2060 consecutive days on Duolingo. During that time I’ve appreciated Duo for the vocabulary but found it very difficult to learn grammar. I’ve got a couple of grammar books (that I don’t have the time to properly study) and I’ve tried several grammar apps (that are characteristically poorly written, poorly explained and generally very unhelpful). I’ve learned more Russian grammar from this app in three days than I have in the past five years. If you’re serious about understanding Russian, this is the best £25 you’ll spend.