ForgetMeNot is a Chrome extension that aims to help you learn new words instead of just looking them up by exploiting the spacing effect.
When you want to look up a new word or a specific concept, use the text box in the plugin to do the site. This will forward your search to your search provider (Google, by default -- check the options page), where you continue your search as normal. However, the extension remembers your search and will remind you to repeat it at predictable intervals in the future.
Studies show that we remember about 10% of what learn in a given day. However, by reinforcing the knowledge we can solidify that knowledge more firmly in the long-term memory. Every time you reinforce the knowledge it will last awhile longer, meaning that you don't have to reinforce it again for longer. The current intervals are as follows and are taken from Paul Pimsleur's research: 2 minutes, 10 minutes, 1 hour, 5 hours, 1 day, 5 days, 25 days, 4 months, and 2 years.
These intervals are just a starting point and will probably change at some point in the future. They can also be customized from the options page.
ForgetMeNot in the Chrome webstore
Author: Jonathan Overholt