Composer

Composer is a tool for dependency management in PHP, inspired by node's npm and ruby's bundler. It allows you to declare, manage and install the libraries on which your PHP project depends. Unlike most package managers, Composer manages on a per-project basis. It installs packages or libraries in a directory (e.g. vendor) inside your project and does not install anything globally. However, for convenience it does support a "global" project via the global command.

Suppose your project depends on a number of libraries which in turn, depend on other libraries. Composer enables you to declare these libraries, finds out which versions of these packages you require, and installs them. You can then update all of your dependencies conveniently with just one command.