Mnemosyne has quite a bit of content, though the quality can be spotty at times: http://www.mnemosyne-proj.org/downloads/cards.php http://www.mnemosyne-proj.org

Mnemosyne has quite a bit of content, though the quality can be spotty at times: http://www.mnemosyne-proj.org/downloads/cards.php http://www.mnemosyne-proj.org/downloads/cards.php Ideally you would want a system (and a license) that allows submitting corrections and updates to the cards.