KDE is mainly known for producing the KDE Desktop Environment (used in Kubuntu) for Linux.
Pixelmator is a popular commercial image editing software for Mac OS X users.
Password Manager, Auto Form Filler, Random Password Generator & Secure Digital Wallet App.
The Raspberry Pi is a cheap, credit-card sized computer. The official website uses phpBB for their discussion forums.
Hugely popular Mozilla community providing support for Firefox, Thunderbird, Seamonkey and other well known Mozilla products. Over 350k members and 4 Million posts.
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.