ProGet vs. Packagist

ProGet helps you package applications and components so you can ensure your software is built only once, and then deployed consistently across environments. This means everyone can be certain that what goes to production is exactly what was built and tested. Third-party packages (such as NuGet, npm, PowerShell, and Chocolatey) and Docker containers are also supported, allowing you to enforce quality standards, monitor for open-source licenses, and scan for vulnerabilities across all packages, much earlier in the development cycle.

Packagist is the default Composer package repository. It lets clients find packages and lets Composer know where to get the code from. Composer can be used to manage your project or libraries' dependencies.