Yes, I think Skritter and Memrise are both ultimately descendants of SRS systems dating back to Supermemo, as Apomixis notes. This would include Anki as well. But I think the execution is sufficiently different that it would be misleading to say they are basically the same thing. From my (vague) recollection, Anki works on a daily cycle; once you finish reviews for the day you won’t see them again. Skritter, by comparison, might show them to you if you went beyond clearing your queue. Welcome anyone to let me know if I’m full of it . . . as I stated my recollection is vague. Also, Memrise has a lot of bells and whistles that might add some value. I have never been a premium user, and some of the features like “speed review” just seem counterproductive in that it would confuse your SRS record.