Actually, to be perfectly clear, OneGet isn't really a package manager.
It's a package-manager-manager -- It's a unified way of installing packages of software regardless of the how-it's-implemented-on-the-back-end.
The first real package provider plugin is a Chocolatey one. Why re-invent the wheel when the wheel already works?
The purpose here is to leverage all these different sources of software using a common set of commands and APIs.
Anything that can be represented as a 'source' of software can be plugged in on the back end. I'm aiming for plugins for NPM, Ruby Gems, Python, on top of the expected MSI, Chocolatey, NuGet, etc...
Plugins can be written by anyone, and I'm going to great lengths to make it as simple as possible -- it's about ~15 or so functions to implement and we can plug in virtually any package format or service into OneGet.