Maybe not - but some tool that you use probably gets it artifacts from it. http://search.maven.org - https://www.quora.com/What-is-the-Maven-central-repository

I'm not saying me having never heard of it makes it less relevant, popular, etc. I'm saying OSS has become so widespread that an entire ecosystem, seemingly with thousands of packages, can exist completely out of my awareness, despite me being involved in OSS for a couple of decades and having much broader (though often not deeper) interests than most, due to my work.

In defense of my ignorance, I haven't written a line of Java in years, and I assume this is a predominantly Java ecosystem (due to the "Maven" part of the name).

Yeah that's true. Think of the npm ecosystem, the burgeoning Go ecosystem, etc. All full worlds with their own repos, etc.