what is the best Q and A wordpress plugin, joomla extension or script?

hi i’m looking to create a niche Q and A site like yahoo answers. I have seen several scripts and plugins but havent seen a truly good one that offers these functionalities:
1. login with openID, facbook connect or twitter
2. share/post question on twitter, facebook

Who knows which script, wordpress plugin or joomla extension offers this?

Thanks!