There are books that teach you how to write Devanagari, for example,
Rupert Snell: Read and Write Hindi Script. Teach Yourself. McGraw-Hill, 2010.
Elvira Friedrich: Einführung in die indischen Schriften. Teil 1: Devanāgari. Third edition. Hamburg: Helmut Buske, 2012.
You can also find many YouTube videos that teach you how to write Devanagari, such as ...
There are three key things to pay attention to (I've found):
place of articulation (~ tongue location)
aspiration (~ whether air comes out while you speak)
voicing (~ whether vocalised - think sneezing 'choo vs. AAH-CHOOOO)
Wikipedia has a convenient table:
of the top row, I think (in my beginners' experience) only nasalisation needs conscious thought, ...
Not what you want to hear, but I don't think you'll find a good learning tool that doesn't require you to learn the script. I'm not a Hindi learner but I have quite a bit of experience learning other languages that use Indic scripts (mostly Thai), and I've seen quite a few people learn those languages with varying approaches to the script and varying degress ...
I have found one free app that at least has a game aspect, although it is not clear whether the entire learning experience is gamified: Learn Hindi™ claims to use an "Addicting game to improve learners' memory" and also contains quiz games. A potential downside is that its primary audience is children.
Other free apps that I have seen don't seem to rely on ...
Rupert Snell's book from the "Teach Yourself" series, Getting Started in Hindi, provides a transliteration for all the Hindi in the book.
That said, he also suggests learning Devanagari:
Although a roman transliteration is provided for all the Hindi in this book, learning to read and write the Devanagari script is extermely worthwhile. Its phonetic ...
Devanagari letter has vowels, Consonants and Compound letters.
alpaprāṇa(very little air flow through mouth) and mahāprāṇa(more air flow through mouth) are types of Consonants which are sounds similar for new learner. ex: Ka(क) and kha(ख)
Compound alphabets look similar for new users, ex: letter ka(क) is compound with e becomes ke(कॆ).
I would like to warn that the Duolingo Hindi app is pretty awful. The audio is really unclear. I had a native speaker listen to it and they couldn't tell what was being said. It's also buggy. Someone on r/LanguageLearning wrote an extensive review detailing its flaws: