(Adding to what you wrote.) Since you mention that it&#x27;s not just for vocab, here&#x27;s an extensive article on how to formulate knowledge in general that goes into a spaced repetition system. (There is also a summary at the bottom.) <a href="http:&#x2F;&#x2F;www.supermemo.com&#x2F;articles&#x2F;20rules.htm" rel="nofollow">http:&#x2F;&#x2F;www.supermemo.com&#x2F;articles&#x2F;20rules.htm</a><p>It&#x27;s part of a site for a closed-source client, but Anki[1] is a good open-source one.<p>[1] <a href="http:&#x2F;&#x2F;ankisrs.net&#x2F;" rel="nofollow">http:&#x2F;&#x2F;ankisrs.net&#x2F;</a>