Brainscape is a flashcard app that uses a Spaced Repetition System, also often referred to as ‘adaptive flashcards’, to help you memorize new vocabulary and facts. It has a team of scientists, engineers, and education experts working to optimize their program for effective learning.
Brainscape is quite similar to Anki, but has a more modern and colourful interface. They also have Certified Classes, which are decks that seem to have been developed by experts in the chosen topic. The app adds what they call Intelligent Cumulative Exposure (ICE) to some of their Certified Classes; it seems to combine a Spaced Repetition System with gradually introducing new concepts, increasing the difficulty of the concepts, and providing context so you can build your own sentences.
It has several Certified Classes for various languages (and other topics), and many more decks created by users. Unlike Anki, edits that creators make to user decks seem to sync up even after you have downloaded the deck.
With the free version, you have limited access to premium decks but unlimited access to user-made decks.