I don’t think there is any single app or website that can give you the full Japanese experience. Japan Activator comes very close, and if you haven’t seen it, check it out.
One of the new entries in the overcrowded “Learn a new language easily at home” category is Fluent Forever.
I have to say, its origin story sounds like a superhero origin. “A young opera singer, surrounded by productions in multiple languages, broke out of his unilingual prison, and developed a method to quickly learn any language.”
It’s a variation on the flashcard theme. You start off by setting your familiarity level with the language. Then, you choose words to create a “grammar” flashcard from. And then, you choose 1-4 pictures to associate with that word. (The latest update lets you create your own flashcards, and also upload your own photos.)
There are also pronunciation lessons, from which you create “listening” flashcards to train your ear. These cards have two similar but different words on them, similar in that the pronunciation of both can be very close.
The listening part is, for me, the most valuable part of the app. It’s really valuable to hear native speakers pronounce words, and for Japanese, with pitch accent.
However, calling them “grammar” flashcards is disingenuous at best. Yes, they do test you on where the word you’ve picked to learn should fit into the sentence, and occasionally they toss in a “dictionary form” at top when the word you’re using is a verb or adjective. But if you’re wanting to learn the intricacies of Japanese grammar, this is not the app for you.
And then there’s a monthly subscription fee after a 14 day trial period, which seems to be a reasonable price to me, but your financial situation might differ.
Overall, I’m keeping it for the pronunciation part. I might outgrow that at some point soon. But for now, it’s valuable. I’ll be interested to see what progress they make.