Anki is the one you are probably thinking about. There are others that do the same kinds of things. These include Mnemosyne ("http://www.mnemosyne-proj.org/ htt

Anki is the one you are probably thinking about. There are others that do the same kinds of things. These include Mnemosyne ("http://www.mnemosyne-proj.org/ http://www.mnemosyne-proj.org/), and SuperMemo ("http://www.supermemo.com/ http://www.supermemo.com/). For a longer list and an explanation of the science behind the software, go to Wikipedia and search for "spaced repetition".