Inspired by Max Berry's book, Jennifer Government, NationStates is one of the most popular online simulation games. The forum boasts over 5 million posts and 200,000 users.
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.
OpenCart is popular, powerful, and easy to use shopping cart software. Their healthy community forums are powered by phpBB.
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.
Pixelmator is a popular commercial image editing software for Mac OS X users.
VirtualBox, developed by Oracle, is cross-platform x86 virtualisation software. It has become one of the most widely used virtualisation solutions in the world.