Warning: This in a very early stage of development. The code works but you can not rely on it. I will add reliability next...
This script is partitioning, formating partitions, downloading a Raspbian Linux Kernel, downloading a Gentoo image and installs it, downloads a portage package tree and finalizes the installation to boot a Gentoo based GNU/Linux operating system on a Raspberry Pi device.
Just insert the SD card after creation into your Raspberry Pi and it will boot a Gentoo OS with a serial TTY enabled and SSH running. Sure, there is some stuff to do but actually it works pretty well.
This project based on the following documentation: