Here are some apps and/or websites I found useful for reviewing/practicing my Japanese:

WaniKani (for Kanji)

JED – Japanese English Dictionary for Android

Jisho – online Japanese dictionary

Obenkyo – for reviewing Kanji, Particles, Vocab and Grammar

HelloTalk – for practising writing/speaking by posting statuses and having them corrected by native speakers

Tofugu – for articles about Japanese grammar points and how to use them


Other useful websites:

Sakura Mobile (for SIM cards and pocket WiFi when you’re in Japan)