Forum Library...

[eluser]mi6crazyheart[/eluser]
I don't know any codeigniter based forum script but here are some popular forum script available on web. Have a look...

* MyBB: http://www.mybb.com/
* punBB: http://punbb.informer.com/
* vanillaforums: http://vanillaforums.org/
* phpBB: http://www.phpbb.com/
* SimpleMachines: http://www.simplemachines.org/