KDE is mainly known for producing the KDE Desktop Environment (used in Kubuntu) for Linux.
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.
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.
Hugely popular Mozilla community providing support for Firefox, Thunderbird, Seamonkey and other well known Mozilla products. Over 350k members and 4 Million posts.
Password Manager, Auto Form Filler, Random Password Generator & Secure Digital Wallet App.
Support for Synology NAS devices and ideas for future versions of the DiskStation software.