I was listening to a dot net rocks the other day where they mentioned, almost in passing, a really intriguing tool for learning new languages -- I think they were specifically talking about F#.
It's a solution you open up and there are a bunch of broken unit tests. Fixing them walks you through the steps of learning the language.
I want to check it out, but I was driving in my car and I have no idea what the name of the project is or which dot net rocks episode it was. Google hasn't helped much. Any idea?