I don't use many apps because my study has become mostly self-directed, but here is what I do use now:
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Anki for flashcards. If you can think of it, Anki has it. Hiragana, katakana, vocab for any level. A great beginner's deck is Kaishi 1.5k. This has a real "gotta keep my streak" feel to it which can be vital to staying on task every day.
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Yomitan and
Yomininja. Yomitan is a browser extension that allows you to highlight any word and instantly pull up a dictionary entry for it, as well as add it to an Anki flashcard deck. Yomininja is an OCR that will allow you to do the same thing but with any onscreen text - I use it a ton for making flashcards from video games.
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Dokidokidict, not related to Doki Doki Literature Club

Similar to yomitan but this one has always-on furigana. If you don't know what furigana is, the simple answer is that it shows you how to pronounce kanji. So this app will let you play Final Fantasy, etc. without having to constantly stop to look up kanji readings.
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Manabi Dojo. This adds Japanese subtitles to many sites (I use it for crunchyroll) and also allows you to pause, highlight words, learn what they mean, etc. Very good if you plan to watch anime.
For study materials, I started with
Learn Japanese With Manga which was super helpful and geared toward beginners. It has a second volume as well, and both are probably easy to find as PDF if you don't want to buy them. I then moved onto
An Integrated Approach to Intermediate Japanese which I adore - it doesn't hold your hand like the first two books I recommended, but I love that about it at this stage.
Last, always feel free to head to
The Japanese Learning subreddit. I don't go here anymore because there are some absolute neckbeard dickheads that will talk down to you for not knowing as much as they do - you know, real "reddit is all I have" types. BUT if you're fine just ignoring that, you can find a lot of great advice here.