Joomla Forums
Joomla is one of the leading open-source Content Management Systems. With a userbase of over 400,000, they use phpBB as a reliable platform for support.
Zend Forums
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.
Bokt.nl
Independent site for Dutch horse lovers. With over 280,000 members and 95 million posts, Bokt.nl is widely acclaimed as one of the largest boards powered by phpBB.
VideoLAN
The VideoLAN project produces the extremely popular VLC media player software. Their forums provide support for users of the software as well as the development community.
Synology
Support for Synology NAS devices and ideas for future versions of the DiskStation software.