[replax]

Yes, Anki used to use a slightly modified version of SM-5 but the Lead-developer decided to revert down to a modified and improved version of SM-2. Basically he reasons (you can find his explanation on the Anki FAQ) that while versions newer than SM-2 are supposed to (slightly) increase efficiency, it only happens if you study every day and at roughly the same time of day. The reason is, that starting with SM-3 a failure on a certain card changes the difficulty of (determined by the algo) similar cards. A further explanation by the lead developer can be found here: http://markmail.org/message/u2zfnrg7x53bzp24#query:+page:1+m... I am convinced that it (at least for me) offers much better studying conditions. (Actually, the mere fact that I can revise on a crowded 30min commute on my ipod would make up for any efficiency increase).