According to Wikipedia, SuperMemo has been available since 1985. Due to its age, it may be the oldest spaced repetition system that is still available. However, was it also the first computer-based spaced repetition system? If not, what was the first one?
(I have checked a few papers on spaced repetition, and these sometimes mention systems such as SuperMemo and Anki, but they did not say what was the first one. Anki is definitely much more recent.)