This document discusses Composer, a tool for dependency management in PHP. It can be installed via curl and used to require packages via the "composer require" command. Composer sources packages from repositories including Packagist, Toran Proxy, Satis, version control systems, and PEAR, although PEAR is discouraged. Toran Proxy is recommended as an alternative to Packagist for being faster, more reliable, and supporting one of Composer's founders for $45/month.