I’m learning Japanese at the moment and this site is really useful, particularly these 100 pages of grammar pointers. I’m leaning in a very grammar-free class but it’s useful to go back and understand why you’re saying things the way you are.
Anki is a really great flashcard timed repetition learning system that runs on your computer, on the web and on your phone. There are thousands of sets of shared flashcards or you can easily create your own. Great for learning a language.
A great app for leaning the Japanese alphabets: Hiragana, Katakana and Kanji. It’s free and very full featured with regular updates by a committed author so consider a donation if it works for you. Thanks to him I can now write the name of the app in Hiragana: おべんきょ
Memrise is a good, if overly animated, site for learning things through flashcards and mnemonics. This course introduces you to one of the basic Japanese writing systems and uses audio which I think is crucial to learning about it.