A WikiForum for exploring/documenting the Linux kernel invites you at http://kernelbook.sourceforge.net/wiki/?KernelWiki.
The Kernelbook project is no longer active and is preserved for research purposes only.
Mmm, my first thought was that a KernelWiki was a Wiki implemented directly in the Linux kernel. Go away, evil thought...
Well, OpenBsd has a HangmanGame build into its KernelDebugger?, where you try to guess global symbols. In old versions `h' meant hangman, not help. This has been changed in 2.2 though.