I'm looking for a web-based system to simply manage libraries as private packages.
From a different perspective it seems you want to build an online repository of JavaScript libraries. I've seen people making efforts to use Maven for JavaScript library management and you would "manage the tangle" with a repository manager (like Nexus or Archiva). I dare say there are other similar offerings if Maven isn't your thing (Gradle, Grapes, Ivy ...).
(Moved from comments, as I thought this wasn't so much seeking clarification as it was suggesting a solution)