Pixelmator is a popular commercial image editing software for Mac OS X users.
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.
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.
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.
It is the Italian Community for Ubuntu, a popular open source community operating system based upon the the Debian Linux Distribution.
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.