whohas is a command line tool that allows querying several package lists at once - currently
supported are Arch, Debian, Fedora, Gentoo, Mandriva, openSUSE, Slackware (and linuxpackages.net),
Source Mage, Ubuntu, FreeBSD, NetBSD, OpenBSD, Fink, MacPorts and Cygwin. whohas is written in
Perl and 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 packages on which the user depends.
* What version of a given package is in use in each distribution, or in each release of a
distribution (implemented only for Debian).