Websites
In order of recommendation...
WaniKani
Focus: kanji
Style: lessons/reviews (SRS*)
Cost: subscription (after level 3)
Bunpro
Focus: grammar
Style: lessons/reviews (SRS)
Cost: subscription (after 30 days)
KameSame
Focus: kanji
Style: reviews (SRS)
Cost: free
Notes:
- inverse of WaniKani for the purpose of practising recall (i.e. producing kanji rather than recognising them or remembering their pronunciation)
- KaniWani is an older alternative - KameSame was created to expand on KaniWani's original inverse WaniKani idea, but I believe KaniWani's scope has broadened since KameSame first built on it
- KameSame can be used for recognition as well, and for kanji not included in WaniKani, but I'd recommend WaniKani first
JapanesePod101
Focus: general (but particularly listening)
Style: lessons (video/audio)
Cost: subscription (some free content)
Satori Reader
Focus: reading (and listening)
Style: reading/reviews (and listening)
Cost: free/subscription for full features
Duolingo
Focus: general
Style: lessons/reviews
Cost: free (you can pay for useless add ons)
Notes: Duolingo doesn't have the best reputation for Japanese,
but it's improved and is fine for some light learning/revision
* 'SRS' means spaced repetition system