An open source set of libraries that can be used as building blocks for an operating system for x86. Includes documentation and publications. http://www.cs.utah.edu/flux/oskit/
Old non-updated mirror online library covering a plethora of OS development topics. Datasheets, tutorials, reference manuals and hardware programming information. http://www.osdever.net/cottontail/
Notes on operating system theory, source code of describing actual construction of operating system in C programming language. Also OS construction related links to books, notes, tutorials, and news groups. http://www.personal.kent.edu/~rmuhamma/OpSystems/os.html