Composer vs Packagist: What are the differences?
Developers describe Composer as "Dependency Manager for PHP". Composer is a tool for dependency management in PHP. It allows you to declare the libraries your project depends on and it will manage (install/update) them for you. On the other hand, Packagist is detailed as "A default Composer package repository". It is the main Composer repository. It aggregates public PHP packages installable with Composer. It lets you find packages and lets Composer know where to get the code from. You can use Composer to manage your project or libraries' dependencies.
Composer and Packagist are primarily classified as "Package Managers" and "Hosted Package Repository" tools respectively.
Composer and Packagist are both open source tools. Composer with 20.5K GitHub stars and 5.56K forks on GitHub appears to be more popular than Packagist with 1.29K GitHub stars and 392 GitHub forks.