NyanNyanVoca
Pick a cat. Get the app.
One language, one character. Both are free on the App Store and Google Play.
Teaches English
CookieNyan English
Illustrated English word cards, varied lessons and Cookie Diary stories. Meet a word, practise it out loud, and collect the scene it lives in.
Teaches Japanese
MochiNyan Japanese
A full JLPT course and a 9,500-word deck, run on a spacing schedule that decides when each word comes back.