Campaign for Gabriel Knight 4 was founded in 2005 by a group of the most devoted GK fans in order to support the 4th part of the game. It is the most famous GK community at the moment.
The site was translated into 11 languages by the fans themselves, and is very informative. You are welcome to join the community and support the project. The Coordinator of the Gabriel Knight 4 Campaign project is Ingrid Heyn aka Almerina.