OpenCart is popular, powerful, and easy to use shopping cart software. Their healthy community forums are powered by phpBB.
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.
A very active community for a KFAN-AM, a popular sports radio station in Minneapolis/St. Paul, MN.
Boasting almost 14 million posts, Ars Technica is one of the biggest and oldest technical forums still operating today. They use phpBB to power their forums and comment system.
Active community for UK based Audi TT owners. Almost 30k members and 2 million posts, complete with unique style & powered by phpBB.
It is the Italian Community for Ubuntu, a popular open source community operating system based upon the the Debian Linux Distribution.