Professional online broker and trading community.
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.
Adblock Plus is one of the most popular Firefox Add-ons in the world, with over 10 Million daily users and over 100k downloads a day. They use phpBB to offer support to their users.
Avant Browser is a fast and user friendly browser which uses Microsoft's Trident rendering engine. The browser has been downloaded over 22 million times.
Fujitsu is a hardware and IT services company focused on providing IT-driven business solutions. Their community forum is powered by phpBB.
The Raspberry Pi is a cheap, credit-card sized computer. The official website uses phpBB for their discussion forums.