When I started to learn about WPF and MVVM recently, I came across some sort of framework or technology in .NET that made it really easy to request a service of some kind. In my particular case, I've got an assembly that handles writing application preferences to an XML file, and I want to let all of my assemblies in the larger application use this to write their own set of preferences to the same file.
I thought it was Unity, but when I looked it up, it didn't seem to be what I read about. The only clue I have for you is that I think it's called a service (it's NOT WCF), and you can request the service two ways: one way gives you the same service each time, like a singleton, and the other way gives you a new instance each time.
Please help to jog my poor memory. :)