Spaced repetition has a pretty good history. If you want a free online alternative, check out memrise.com. They're pretty popular in the language learning commu

Spaced repetition has a pretty good history. If you want a free online alternative, check out memrise.com. They're pretty popular in the language learning community, but they cover a lot of areas and you can create your own. For example, here's there physics section: http://www.memrise.com/courses/english/physics/ http://www.memrise.com/courses/english/physics/