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.
Fujitsu is a hardware and IT services company focused on providing IT-driven business solutions. Their community forum is powered by phpBB.
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.
Password Manager, Auto Form Filler, Random Password Generator & Secure Digital Wallet App.
Hugely popular Mozilla community providing support for Firefox, Thunderbird, Seamonkey and other well known Mozilla products. Over 350k members and 4 Million posts.
KDE is mainly known for producing the KDE Desktop Environment (used in Kubuntu) for Linux.