
WaniKani is a web application for learning Japanese kanji and vocabulary with the goal of teaching you around 1,700 kanji and 5,000 vocabulary words in about a one to two years. "What? That's impossible!" you scream. "Okay, tell me more," you continue after calming down.
It uses their own homebrew of radicals, mnemonics, space repetition system, and a kanji ordering that allows you to learn much more quickly and effectively compared to the traditional methods. At least it's working very well for me.
Most kanji learning is broken and inefficient. They want to fix that.
It is possible to try out the first three levels completely free of charge.