symboldrill is a free set of drills for learning Japanese. It's built to be fast, to work on phones, and to keep your progress in your browser, with no accounts.
Kanji meanings, readings, grades, and frequency ranks come from KANJIDIC2, and example words come from JMdict. Both are by the Electronic Dictionary Research and Development Group, used under CC BY-SA 4.0.
More subjects are planned. Feedback and corrections are welcome: see the contact page.