I came across this article on Facebook:
Free and Equal Elections Foundation announced today that four candidates have confirmed their participation in the 2012 Presidential Debate at the University Club of Chicago on October 23: Libertarian Party candidate Gary Johnson, Green Party candidate Jill Stein, Constitution Party candidate Virgil Goode, and Justice Party candidate Rocky Anderson.
This debate is the only 2012 Presidential Debate featuring four candidates. The top six candidates were invited to participate. Democratic Party candidate and incumbent Barack Obama and Republican Party candidate Mitt Romney are welcome to participate in this historic debate. The moderator will be announced shortly.