In 1985 (!) he wrote SuperMemo, a piece of software that utilized this spacing effect:
"SuperMemo is based on the insight that there is an ideal moment to practice what you've learned. Practice too soon and you waste your time. Practice too late and you've forgotten the material and have to relearn it. The right time to practice is just at the moment you're about to forget. Unfortunately, this moment is different for every person and each bit of information."
The full article is a bit long but if you're interested in this stuff, it's well worth the read.
SuperMemo seems to have fallen behind as far as software goes, but there are great alternatives, like Anki  that use the same method.
The method I described is from a Lifehacker post earlier this year.
As an aside, Anki is excellent. In the past few months version 2.0, a new version deserving of a major version number, was released for Windows/Mac/Linux, and just recently for iOS. The corresponding Android version is a little behind but I imagine it will be out soon too.