There's this fairly popular one that I'm using right now, and it's made to be a bit like Duolingo except for a language that's not on Duolingo. Buuut it doesn't have any form of spaced repetition. Training is just "select the chapters you want to be quizzed on". And of course you can't export the vocabulary, presumably so you stay inside the app and pay for premium which unlocks study games, which, afaict, are not spaced repetition based either.