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.
Solia Online is one of the most active online communities with over 18 million posts. Solia Online allows you to create your own avatar, buy items, and discuss topics with your friends.
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.
As the official board for the world-famous band Queen, this community hosts a wide variety of discussions by Queen fans from around the globe.
Conquer Club is an online multiplayer world domination game. The discussion forum is host to over 500,000 members and 2.8 million posts.
KDE is mainly known for producing the KDE Desktop Environment (used in Kubuntu) for Linux.