That is a long story. I was a contributor and moderator on another atheist site. There was some friction between moderators, so four of us got together and created Atheist Universe. Two still remain active, doone and myself, the other two are involved in other projects at the moment.
You see their work every time you log in though, Michel designed the site and Adriana's Science Fix and Morality discussions are still going.
Of course, we're here because we are non-believers in a land where we are the minority, and sometimes you need a dose of reality. =)