Review of Mnemosyne vs. Anki vs. SuperMemo http://nihongoperapera.com/mnemosyne-anki-review.html
Open Source Anki: http://en.wikipedia.org/wiki/Anki
Open Source Mnemosyne: http://en.wikipedia.org/wiki/Mnemosyne_(software)
Some science: http://en.wikipedia.org/wiki/Forgetting_curve
http://en.wikipedia.org/wiki/Spaced_repetition
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And my favorites for language learning: http://www.smart.fm/