probably just about 0% of the viewers of this webbed site are learning japanese so i predict that this list will not be useful to anybody at all, but there's no harm in putting it here anyways. all of these recommendations should be taken with a grain of salt. (just found them by chance mostly & kept what seemed good)
you can find a lot more resources and such over at tofugu.
- anki is an extremely versatile flashcard app which uses spaced repetition to choose what to review. spaced repetition is incredibly useful for memorization and recall; read more in this excellent article by Nicky Case. anki is very powerful--cards can use arbitrary HTML and CSS, have images/audio embedded, etc., you can customize how often cards are shown, there are tons of addons to help your workflow, and all of it is designed with flexibility in mind (which does come at a cost of ease of use for simple use cases, and aesthetics (unless you like your default system theme)). it's been probably the most useful tool for me for learning japanese and as long as you can tolerate a bit of involved setup and manual-reading (very important to read the manual first of you'll get confused) i highly recommend you try it out. totally free except for the iphone app which costs $25.
- core 2k/6k is a vocabulary deck for Anki that has a pretty good word selection and includes sentences and audio for both words and sentences.
- wanikani is a popular platform for learning kanji and related vocabulary using spaced repetition (again). it seems pretty great but costs a lot of money, but you can get a similar service for free (as long as you don't care about not giving the people who should be getting money money) by downloading an anki deck. there's one listed on ankiweb but a newer one exists online, called "WaniKani Ultimate 3: Tokyo Drift". seems to only be available through a discord server but definitely works (or just use the one on ankiweb it's not that much worse). tofugu seems like a pretty cool company though so if you can afford it i'd recommend paying for the actual platform. alternatively you can just do the first 3 levels for free which is still a good start for learning kanji.
- bunpro is yet another spaced repetition-based platform, this time for grammar. it has a 1-month free trial (without having to set up payment! very nice) and in that 1-month period you could learn 1-2 of the units (N5 through N1, roughly corresponding to JLPT), or 3 if you're really pushing it (12-16 new grammar points per day). also seems fairly affordable after that esp. when you'll only need it for a few months.
- tae kim's guide to learning japanese is a pretty good online textbook of sorts. starts from zero (teaches hiragana & katakana, plus proper pronunciation).
- there are also a lot of physical textbooks to choose from but i can't give any recommendations because i've almost entirely been using online resources. anything in print is probably more reliable.
- duolingo is lacking in some areas (it's a pain to start with because they don't teach kana well, it's prone to having misleading information, it's not excellent for learning and works best with other practice). it's certainly an option but i wouldn't recommend using it exclusively.
- kakimashou is a web app that lets you practice writing kanji (and kana) with correct stroke order. while it's probably not well-advised to learn kanji this way it's great for practicing kanji you already know & review.
- nhk easy is a news site aimed towards children and japanese leaerners. includes furigana (can be switched off) and definitions for a few words.
- yomujp looks pretty good but i haven't used it much. articles are grouped by JLPT level, plus an N6 category for things easier than N5.
- anki deck with all the lines of dialogue in persona 4. i don't know if this really fits in this category, but if you've ever wanted to read every line of dialogue in persona 4 in random order multiple times, or you think this could help you learn (probably could), you should check it out.
- go play deltarune in japanese. or like, any other game that has a good jp translation. i think deltarune's pretty cool so that's the first one that came to mind. of course you'll probably need to get to like N4-N3 level to work through it (at least that's my current level and i can read it with effort. there's probably More Advanced Things going on but you can learn those by reading! i guess!)
other games / media i have looked at:
逆転検事２ (ace attorney investigations 2): ace attorney game, only released in japan. it's pretty much the same as any other ace attorney game but with a slightly shorter gameplay loop. probably all the things i'm saying here apply to the other games in the series (if you haven't played any of the games, the original trilogy would be a good starting place). as for usefulness as a learning resource,
- since it primarily involves finding contradictions in testimony etc., you have to Actually Understand the things people are saying and Pay Attention to things instead of, blacking out and pressing through lines of dialogue without fully comprehending them. (except that there are a lot of places where the game literally tells you what to do. maybe that's only in the first two cases)
- as for difficulty, i've been doing pretty alright (although i had to look up around 360 words in the first two cases of five) at around a jlpt n3 level. mostly been having trouble with vocabulary rather than grammar, seems like the grammar is relatively simple (makes sense because each line has to be like 20 words long at most)
- different speech styles for different characters, although it doesn't really seem to reflect how people would actually talk (afaict, i don't really know much about this kind of thing)
- fairly engaging, game frequently makes you do a thing instead of just being listening to people talk for an hour. although there were some parts that felt like listening to people talk for an hour, especially at the end of chapters. (i mean most of the gameplay is reading anyways. some looking as well i guess)
- i have not been doing enough reading/listening practice at all so currently this list has precisely one item on it. once i'm finished with aai2 i'll probably do the fifth and sixth games in the series that supposedly nobody likes, and at the rate i've been going i'll be finished with all three games, in a year maybe?
- 逆転検事２ (ace attorney investigations 2): ace attorney game, only released in japan. it's pretty much the same as any other ace attorney game but with a slightly shorter gameplay loop. probably all the things i'm saying here apply to the other games in the series (if you haven't played any of the games, the original trilogy would be a good starting place). as for usefulness as a learning resource,
- again, you can find a lot more resources on tofugu. they probably know a lot more about this than i do.
- jisho.org is an online dictionary which compiles a bunch of different source dictionaries and gives them a pretty nice frontend. while some of the features are a bit lacking & the search query system is fairly limited it's great for looking things up.
- yomichan (firefox, chrome) allows you to hold down a modifier key while moving your mouse over japanese text to look up words, generally really convenient. using some other pieces of software you can even add vocabulary you don't know into your anki collection.
- japanese (google play, app store) is a dictionary app for mobile. comes with a spaced repetition-based learning & review feature but you might as well just use anki for that. unless you don't want to mess with anki of course. (update: i've actually been using the japanese app for vocabulary found in media, because usually if i'm on a computer it's easiest to look up a word on my phone instead of switching windows, and just hitting "add to deck" on every word you look up is really convenient. depends on your workflow i guess. some people have this whole ass setup where they have the subtitles to the anime they're watching downloaded, and whenever they hit a word they don't know they just hit a button and it creates an anki card with the word, a definition, a screenshot of the anime, a recording of the sentence where the word is used with subtitles, maybe more. i don't do that. i used to manually type out context sentences on each word i looked up (the app has a thing where you can add notes to words), but i stopped doing that because it was kind of tedious and there wasn't much point in it. point is that you should just do whatever works, and most things will work)