When I was browsing Hacker News today, I stumbled upon a neat Org mode extension called org-drill. The idea is that it implements an electronic version of flash cards that are useful for learning vocabulary or other facts. Obviously, this is mostly useful to students but anyone who is trying to learn a set of related facts would probably find it useful.
This is a pretty sophisticated package that uses a spaced repetition algorithm to optimize learning the material and that has several different modes for presenting the questions and answers. The questions and answers are, of course, plain text org files so they're easy to set up and modify. The page at the above link discusses the different modes in detail and is worth taking a look at if you think you might be interested in something like this.
Setup is a breeze. The
org-drill.el file is part of the contributed packages so you just need to add a pointer to that directory to your Emacs
load-path if you don't already have one and then add
init.el file. You can also enable it with the customize interface if you prefer. The details are on the org-drill page.
The org-drill package is another example of the power and flexibility of Emacs and Org mode.