Official Support Forum for Debian, the kernel-based open source operating system. phpBB provides a solid platform for support and discussion.
Zend Technologies is one of the largest and most popular companies producing a wide variety of tools and frameworks for PHP. Their community forums rely on phpBB.
Developed by Focus Home Interactive, Cities XL 2011 is a city simulation game. Their community forums are powered by phpBB.
Hugely popular Mozilla community providing support for Firefox, Thunderbird, Seamonkey and other well known Mozilla products. Over 350k members and 4 Million posts.
Discussion board for the massively popular xkcd web comic. Covering everything from Maths and Science to Logic Puzzles and Forum Games. Over 100k members and 2.4 Million posts.
OpenCart is popular, powerful, and easy to use shopping cart software. Their healthy community forums are powered by phpBB.