Fujitsu is a hardware and IT services company focused on providing IT-driven business solutions. Their community forum is powered by phpBB.
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.
OpenOffice.org offers a free and fully-featured office suite which meets the needs of the common consumer all the way up to large enterprises.
KDE is mainly known for producing the KDE Desktop Environment (used in Kubuntu) for Linux.
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.
Active community for UK based Audi TT owners. Almost 30k members and 2 million posts, complete with unique style & powered by phpBB.