Pacman Home Page
pacman is a utility which manages software packages in Linux. It uses simple compressed files as a package format, and maintains a text-based package database (more of a hierarchy), just in case some hand tweaking is necessary.
pacman does not strive to "do everything." It will add, remove and upgrade packages in the system, and it will allow you to query the package database for installed packages, files and owners. It also attempts to handle dependencies automatically and can download packages from a remote server.
History
Version 2.0 of pacman introduced the ability to sync packages (the --sync option) with a master server through the use of package databases. Prior to this, packages would have to be installed manually using the --add and --upgrade operations.
Version 3.0 was the switch to a two-part pacman — a back-end named libalpm (library for Arch Linux Package Management) and the familiar pacman front-end. Speed in many cases was improved, along with dependency and conflict resolution being able to handle a much wider variety of cases. The switch to a library-based program should also make it easier in the future to develop alternative front ends.
Version 4.0 added package signing and verification capabilities to the entire makepkg/repo-add/pacman toolchain via GnuPG and GPGME.
Version 5.0 added support for pre/post-transaction hooks and sync database file list operations.