WaniKani - Learn around 1,700 kanji and 5,000 vocabulary words in about a one to two years.

Kanjidon - Collect Cards. Remember Kanji.

Kanji Koohii - Remember the kanji; mnemonics, smart dictionary, flashcards, spaced repetition.

Kanji Dojo - Android application for practicing writing Japanese characters

Kanshudo - Master kanji, hiragana and katakana, along with Japanese grammar and vocabulary.

Anki - Anki is a program which makes remembering things easy. Because it's a lot more efficient than traditional study methods, you can either greatly decrease your time spent studying, or greatly increase the amount you learn.