|...is a new hybrid Operating System and Desktop built from the best parts (IMHO) currently available.
The Linux kernel is probably the best bet at the moment, although a micro-kernel could unseat it. Currently my own beef with the Linux is that quite often to access some functionality of your hardware you need to recompile.
Reiser4 sounds like it's nailed about 90% of what I want in a file system. My only concern is that it lacks BeFS's live queries which just plain rock. BeFS would be a great fall back.
X11 is way too slow, Windows is closed source, BeOS's GUI is closed source. Bascially there is nothing out there to run the GUI that is modern, fast, cross-platform, flexible and available... better write one. My guess is that the best option would be using something like directfb or SDL to write a MacOSX like GUI, lots of hardware acceleration, transparency, animation, neat effects, easy to use API in C/C++. Then for application support a Xlib wrapper would work just fine.
BeOS got it right with their desktop. And it's kinda available in open source projects. Although much API hackery would be needed to shoe horn it into Linux / Reiser4.
So I'm just missing a GUI for my frankenstein OS... *twiddle twiddle*