Interested in going to medical school? You may be interested in checking out SpacedEd.com. The site, created by Harvard Medical School professor B. Price Kerfoot, claims to help you "learn most anything in 3 minutes a day." You'll be emailed questions once a day that ask you questions related to whichever topic/course you select. The best part: it's free.
Right now, most of the topics are science related, although there are also "courses" on other topics, such as "iPhone Tips and Tricks" and "Bartending 101."
(Full disclaimer: Dr. Kerfoot and I were colleagues in our Master's program at Harvard.)

