A good open source for a forum.

[AH - George]

SMF feels old fashioned IMHO. phpBB or MyBB, I like those two. Both phpBB & MyBB released new versions of their software fairly recently, both pretty nice little updates I believe.

[linkalone]

MyBB it's free and looks more like vBulletin (NR.1 forum platform). Some issues regarding the spam, but if you know how to handle this, you'll be fine.

[Ixam]

MyBB is much better than SMF in my opinion.

[standingoten]

phpBB is probably the better forum script out of the optioned mentioned. The developers that make add ons and templates are countless along with the security upgrades.

[OurInternet]

As for me SMF is nice for forums