This app was mentioned in 3 comments, with an average of 2.00 upvotes
I love this app: Fun Easy Learn Russian. It has a large variety of vocab broken down into categories and several different exercises per category - matching the word to an image, audio & spelling practice, etc. The variety keeps me interested whereas things like Memrise and flashcards bore me to tears. Of course, I know everyone is different, but they just don't work for me except in very small doses.
The free version of the app does have some ads, but I don't find them too intrusive. The paid version is ad-free and costs $11.99.
If this app had grammar practice & sentence building, it would be perfect in my eyes. That's a drawback for sure. But for vocabulary alone I think it's fantastic.
I use this app for learning words. It comes in 3 "difficulties" so to speak, so you can accomodate your vocabulary from simple to more complex. Altough learning and reading cyrillic is no small matter, if you don't get the grammar you won't get very far, so I suggest you also check the Russian Grammar Wiki too learn a little about the nouns and adjectives formulae and times of words.
And finally, don't just stay with books, but diversify! Use Youtube to listen to music, watch videos, try to watch movies and read children books to get a feel of the most basic phrases, once you can read a whole kiddy book in russian without looking at the dictionary you have already mastered basic russian and can hold a conversation.
Oh! and if you want you can also try to translate book or song. I'm currently translating Crime and Punishment by Dostoevsky and it helped me greatly (And haven't even finished chapter 1).
Προσωπικά έχοντας δοκιμάσει και το Duolingo και το FunEasyLearn προτιμώ το δεύτερο. Μοιάζουν (έχουν gamification και τα δύο), αλλά το δεύτερο σε μαθαίνει να γράφεις σωστά και την αλφαβήτα (νομίζω και τις δυο γραφές: printed & cursive):