Kanji Ryokucha provides a native interface to your SRS kanji reviewing at Kanji Koohii (kanji.koohii.com).
Important: you need a Kanji Koohii account to use this app.
Kanji Koohii implements the spaced repetition system as a complement for James Heisig's method from the book Remembering the Kanji.
Kanji Ryokucha is an independent app that uses an API provided by Kanji Koohii for this purpose. It is 100% free, no ads, no strings attached.
Happy reviewing!
Very useful. Perhaps some options to change pen thickness would be usefull but otherwise great app.