.NET software architecture with in-process pub/sub in mind

Is there anything like an in-process pub/sub pattern to provide lose coupling in an application? Is there a design pattern for that? Or framework?

I want all classes to know the broker and subscribe to topics. I don't want classes to know about each other. pub/sub comes to mind. Or message oriented middleware. However I couldn't find any frameworks for that.

Are there any design patterns you can recommend? Or Framework?
I did find ZeroMQ which looked rather complex.

Otherwise I'd go with a Producer-Consumer pattern and build something upon that.