zkanji - zkanji is a free and open-source study tool and dictionary of the Japanese language.
Kanji Koohii - Remember the kanji; mnemonics, smart dictionary, flashcards, spaced repetition.
RomajiDesu - RomajiDesu is a free online bi-directional Japanese-English dictionary, Kanji dictionary, Sentence analyzer and Japanese to Romaji/English translator, and Romaji to Hiragana/Katakana Converters for Japanese learners.
Duolingo - Duolingo is a free language learning app for iOS, Windows and Android devices. The app makes learning a new language fun by breaking learning into small lessons where you can earn points and move up through the levels. Read more about Duolingo.
JDICT - JDICT is a cost-effective application that provides you an opportunity to convert the Japanese text into English, making you easily communicate with your friends without any disturbance.
WaniKani - Learn around 1,700 kanji and 5,000 vocabulary words in about a one to two years.