This is really great! I'm building a SaaS that is similar to this, but I was feeling bummed about not releasing it as open source; but now I can just point people to this if they want to run their own. awesome!
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The only novelty on my app is that it uses an algorithm based on upvotes/downvotes (e.g. HN, Reddit, etc) to measure card performance rather than a variant based on SuperMemo and friends.
I already wrote a spec on it (feel free to steal =P): https://github.com/grokdb/spec
That said, if you're up for beta access, shoot me an email at r.letmein [a] ruru.name and i'll see about access