LinuxKernel is a free UnixLike kernel, originally created by LinusTorvalds in 1991. The GnuLinux OperatingSystem now benefits from the contributions of millions of users and developers around the world. Developed under the GnuGeneralPublicLicense, the SourceCode for GnuLinux is freely available to everyone. For more information on GnuLinux try http://www.linux.com/ or http://www.linux.org/
See also http://www.kernel.org/
to compare and contrast, see GnuHurd
For some reading see UnderstandingTheLinuxKernel.
For a new web enabled tool for configuring and editing the Linux Kernel see LinuxGuru.