Metro is a build tool that can build Gentoo Linux OS releases and OpenVZ
templates. It’s designed to interface with a package manager such as
Portage/emerge so that users can build their own releases of Gentoo or
other Linux-based operating systems.
The heart of Metro is its data-oriented recipe language and associated
parser, which has been designed to keep operating system builds
organized, consistent, maintainable and reliable.
From a Gentoo perspective, you can view Metro as a complete re-thinking
and redesign of Gentoo’s Catalyst build tool – building on its strengths
and addessing its weaknesses.