Apps similar to Kanjidon include Anki, which is free and open source. Other options are Kanji Dojo, WaniKani, Kanji Garden and KanjiTomo. In total there are seven Language Learning Tools like Kanjidon for the web, Android, Windows, Linux and iPad.
Anki is a program that makes remembering things easy. Because it is a lot more efficient than traditional study methods, you can either greatly decrease your time spent studying or greatly increase the amount you learn.
Australia
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.
United States
Teaches Kanji while also giving interesting origins of the kanji. Available as website and Android/iPhone apps.
KanjiDraw is a browser-based Japanese writing practice tool. Each kanji progresses through stroke-order puzzles, guided tracing, free drawing, and multi-size drills.
Italy
EU
Nihongo Master is an online Japanese learning platform for beginners through advanced learners.
United States
