Operating SystemsFirst of all, some links to collections of OS references. Following these links, you can find any existing OS:
If you want to create a your own operating system, look at the SigOps page about it.
Some vertically structured OSs: FreeDOS project.
The SHARK kernel is based on a preliminary version of OSLib.
ProgrammingFirst of all, a good C/Unix course; links to other programming sites are coming soon.
PhilosophyHere, you will find some links about free software and related arguments. The most important is the GNU Philosophy Page. Another interesting site is the Open Source Page.