The Linux kernel is an operating system kernel used by the Linux family of Unix-like operating systems. It is one of the most complex & prominent examples of free & open source software.
This Interactive Map of Linux Kernel gives you a graphic view of the Linux Kernel. You might want to check it out as it is prety interesting and informative.
You can drag and zoom the image and see the important modules in it. Each important item on the map is also linked to a webpage which gives further details on it.
Check out the Interactive map of Linux Kernel at MakeLinux.net.