Jascha Wetzel's _(XOS | http://free.prohosting.com/~xos/) aims at being an _(OO), _(distributed), preemptively multitasked/threaded, message-passing based system. While this would sound like pretty standard marketroid talk, the site contains very interesting, detailed and clear documentation about what the author has in mind, an _(object-oriented) _(microkernel) where every part of the system does one thing and does it well, without any of the other parts knowing the details; a definite plus for scalability and future expansion. The author also cares to define the concepts he uses, so have a look at it even if you don't do _(C++) in your sleep. The actual implementation hasn't started yet, but definitely a spot to watch.