The GNU project were early promoters of open source operating systems and software. It launched in 1984 to develop the GNU operating system, a complete Unix-like operating system which is free software. That is software which respects your freedom as well as being open source. What is known as Linux could most accurately be called GNU/Linux. That is the GNU tools with the Linux kernel. GNU are also developing their own kernel called Hurd.

GNU homepage

Hurd kernel