whohas

query multiple distributions' package archives
whohas is a command line tool that allows you to query several package
collections at once.
.
It supports Arch Linux (and AUR), Debian, Fedora, Gentoo, openSUSE, Slackware
(and linuxpackages.net), Source Mage Linux, Ubuntu, FreeBSD, NetBSD, OpenBSD,
Fink, Mandriva, MacPorts and opkg (OpenMoko community) repositories.
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whohas was designed to help package maintainers find ebuilds, pkgbuilds, and
similar package definitions from other distributions to learn from. However, it
can also be used by normal users who want to know which distribution provides
certain packages, and which version of a given package is in use in each
distribution or in each release of a distribution.