The Free Software Foundation or FSF is at http://fsf.org
It is also sometimes called GNU after its original project, "GNU's Not Unix." It uses a gnu-head as its symbol. It is identified with Richard Stallman, who is approximately as stubborn as any hoofed animal imaginable.
The FSF wrote the GPL and GFDL and takes some responsibility for their enforcement, although it is often criticized for having no viable way to do this in a self-funding manner. Some believe they have done an inadequate job for instance of getting GFDL corpus access providers to cooperate and integrate and annotate material consistently as the GFDL itself requires - an issue of some interest to CGO especially re Research Wiki integration.
The open source and some consortia (like W3 and Java) were both responses to issues with GPL, and other aspects of FSF's ideology and solutions. Creative Commons was likewise inspired by, but critical of, GFDL. See problems with free software and open source models for more.