Dresden Real-Time Operating System Project (DROPS)
http://os.inf.tu-dresden.de/drops/

GNU Mach
http://www.gnu.org/software/hurd/gnumach.html

Fiasco u-kernel
http://os.inf.tu-dresden.de/fiasco/overview.html

fusd
http://www.circlemud.org/~jelson/software/fusd/

hurd.in
http://hurd.in/bin/view/Hurd/WebHome

kdb
http://oss.sgi.com/projects/kdb/

Kernel Newbies
http://www.kernelnewbies.org/

Kernel Rebuild Guide
http://www.digitalhermit.com/linux/Kernel-Build-HOWTO.html

L4 Environment
http://os.inf.tu-dresden.de/l4env/

L4Ka Pistachio microkernel
http://l4ka.org/projects/pistachio/

Linux Kernel Cross-Reference
http://lxr.linux.no/

Linux Kernel Archives
http://kernel.org/

Linux-mm
http://linux-mm.org/

OSSO microkernel OS
http://osso.sourceforge.net/

Philip's Kernel Compilation
http://www.linuxfocus.org/English/July2002/article252.shtml

Understanding the Linux Kernel Virtual Memory Manager
gorman_book.pdf