phpBB3 

A next-generation forum script with better security then it's predecessor, phpBB2. It's a free script that has been downloaded millions of times and used on an estimated 6 million websites. A webmaster could easily find modifications (MODs) to add features and even free web templates for your forum (styles). The project is run by the phpBB Group and they always release under the GPL license.

An example site that uses phpBB3 is www.phpBB.com

phpBB3 by Yukan May 6, 2008

phpBB 

Short for PHP Bulletin Board. A free forum application written in PHP and developed by the phpBB Group. It is distributed under the GNU GPL license and is available for download from phpbb.com

Our forum is powered by phpBB.

phpBB by jleq July 16, 2003

phpbb 

best thing ever.

oops, phpBB stamped on IPB and vB then forced them to eat each other's shit, vomit it up and eat it again.

phpbb by roofles March 31, 2004

phpBB 

Very good message board system.

Oh no! Ezboard's advertisements caused a malfunction in my system! Time to get a phpBB2 forum!

phpBB by Weewan is Crap November 2, 2003