There is one more alternative

[kferrone]

Hi, didn't know where to leave you a simple comment so I posted here.

In the docs there is this section: Sinopia Similar Things

At the very bottom under Similar Existing Things, you ask if there is more. There is one more and it's called Artifactory by JFrog.

Here is the link: https://www.jfrog.com/artifactory/

Unfortunately the NPM repos are part of the pro plan, not the open source. The open source version only seems to support Maven. Either way it's the only other option for a private NPM repo that you have not covered in your list that I've seen.

[Delagen]

Nexus has free version

[kferrone]

mmmm thank you @Delagen Nexus looks super legit!

[jhfoo]

Sinopia lives through a fork: https://github.com/verdaccio/verdaccio