So I'm building Amgi (암기, means memorization in Korean), an open-source plain-text spaced repetition system with FSRS. I started building it only a week ago.
Flash cards are simply Markdown files with pretty elegant syntax, so you are not tied to any app. Just open your flashcards folder in your favorite editor and add/edit straightaway:
Q: What does FSRS stand for?
A: Free Spaced Repetition Scheduler
C: The capital of [France] is [Paris|city].
Amgi has a dashboard where you can see your streak & some statistics on your reviews, and a browser where you can search using queries similar to Anki's (deck:Name, #tag, is:due, etc.). It also supports LaTeX, images, audio and code blocks (incl. making cloze cards inside of them). And it has a cute installer! (I hope)It can already import from Anki, but it's still pretty early and the only Anki collection I've tested on is my own, so expect some rough edges. Mac-only for now!
My own collection is public too, it's the actual one I use daily: https://github.com/alisheryeginbay/flashcards
Would love feedback, especially on the card syntax :)