I'm working on Phrasing.app that does just this. We originally used ebisu, but ended up (heavily) modifying our own fork of FSRS. We don't use due dates really

I'm working on Phrasing.app that does just this. We originally used ebisu, but ended up (heavily) modifying our own fork of FSRS. We don't use due dates really (except for some analytics by request), but instead try to keep a user at various difficulty levels. We care more about forward progress then making sure you're always 100% caught up (if a words really that important, you can either favorite it or you'll see it again). It's not an open flashcard app, we're really also heavily focused on automatic sentence mining for foreign languages, but I'd be happy to answer any questions about my experience adapting FSRS. You can see more about the product at https://blog.phrasing.app/phrasing-first-look/ https://blog.phrasing.app/phrasing-first-look/