* [http://www.chromium.org/chromium-os/developer-guide/chromite-shell-quick-start chromite] build utility from chromium os ([https://chromium.googlesource.com/chromiumos/chromite/ source repo])
** as far as I recall chromium os does highly parallel building making their build really fast with a slight trade of in long termn stability (ie. build might fail due to dependencies being built out of oder),
** the [http://www.chromium.org/chromium-os/developer-guide chromium os developer guide] might also be of interest, among other things it shows that google do split the build into a package building part and an image creation part.* [https://wiki.sabayon.org/?title=En:Entropy entropy] is sabayons portage replacement, it focuses on binaries due to sabayon being a binary distribution** their build system "Matter" might be of interest (although I haven;t found any info), also sabayon has <code>kernel-switcher</code> for updating kernels** kernel ebuilds live [https://github.com/Sabayon/sabayon-distro/tree/master/sys-kernel/linux-sabayon here] and probably rely on the [https://github.com/Sabayon/sabayon-distro/blob/master/eclass/sabayon-kernel.eclass sabayon-kernel eclass].
==== "stage4"/box/iso building ====