Package Manager Specification

The Package Manager Specification is a standardization effort to ensure that the ebuild file format, the ebuild repository format (of which the portage tree is Gentoo's main incarnation) as well as behavior of the package managers interacting with these ebuilds is properly written down and agreed upon.

By defining the ebuild format and package managers behavior, it is possible for software developers to create other package managers next to Portage that are fully compatible with the ebuilds and as such can be used on Gentoo (and related) distributions.

For more information, see Gentoo's Package Manager Specification project.