Wikipedia
PackageKit is a free and open-source suite of software applications designed to provide a consistent and high-level front end for a number of different package management systems. PackageKit was created by Richard Hughes in 2007, and first introduced into an operating system as a default application in May 2008 with the release of Fedora 9.
The suite is cross-platform, though it is primarily targeted at Linux distributions which follow the interoperability standards set out by the freedesktop.org group. It uses the software libraries provided by the D-Bus and Polkit projects to handle inter-process communication and privilege negotiation respectively.
Since 1995, package formats have been around, since 2000 there have been dependency solvers and auto-downloaders as a layer on top of them around, and since 2004 graphical front-ends. PackageKit seeks to introduce automatic updates without having to authenticate as root, fast-user-switching, warnings translated into the correct locale, common upstream GNOME and KDE tools and one software over multiple Linux distributions.