Memorion is a free Android flashcard management system based on spaced repetitions, many games and a very flexible configuration, working completely offline. It is a non-profit project that I am working on since 10 years.
Memorion has been updated, the import of Memrise cards has been simplified (unfortunately the learning progress cannot be imported).
App: https://play.google.com/store/apps/details?id=com.MemorionSoft.MemorionV2
Intro Video: https://www.youtube.com/watch?v=BukBnA28Fvs