Portage is a package management system used by Gentoo Linux, based on the concept of ports collections. Gentoo is sometimes referred to as a meta-distribution due to the extreme flexibility of Portage, which makes it operating-system-independent. The Gentoo/Alt project is concerned with using Portage to manage other operating systems, such as BSDs, Mac OS X and Solaris. The most notable of these implementations is the Gentoo/FreeBSD project.
There is an ongoing effort called the Package Manager Specification project (PMS) to standardise and document the behaviour of Portage, allowing the ebuild tree and Gentoo system packages to be used with alternate package managers such as Paludis and pkgcore. Its goal is to specify the exact set of features and behaviour of package managers and ebuilds, serving as an authoritative reference for Portage.