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Said about Cloudsmith as an alternative
Cloudsmith provides full compatibility with npm (and npmjs), but as a full package management SaaS alternative. It has support for package formats beyond npm alone (such as Python/Ruby), and brings a whole suite of features that would be interesting to polyglot users, orgs and environments.
Packagist is fantastic (of course) as a Composer service, but Cloudsmith offers a universal approach to package management across many different types of package formats - It might be more appropriate if you're using more than just PHP/Composer technologies.
Like GemFury, Cloudsmith is a universal package management service, with more than just support for Rubygems. Customers love Cloudsmith because of the focus on simplicity and the ethos of being as secure as possible by default. It also has a generous free tier, and is completely free for open-source.