[Packagist](http://packagist.org/) is the main composer repository. A composer repository is basically a package source. A place where you can get packages from. Packagist aims to be the central repository that everybody uses. This means that you can automatically `require` any package that is available there.
If you go to the [packagist website](http://packagist.org/) (packagist.org), you can browse and search for packages.
Any open source project using composer should publish their packages on packagist.
## Autoloading
For libraries that follow the [PSR-0](https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-0.md) naming standard, composer generates