Zìzài 字在

Chinese, at ease.

Chinese flashcards that come back just before you'd forget. HSK 3.1, offline.

Get it on Google Play Free, for Android.

A review in Zìzài: the card for 没关系 (méiguānxi, "it doesn't matter") with its traditional form 沒關係, above four buttons that say when the word comes back.