MEF: Microsoft's Managed Extensibility Framework

Krzysztof Cwalina announced that Microsoft has released a CTP of its Managed Extensibility Framework (MEF).

MEF is basically a dependency injection framework that allows to provide extensibility for your applications (add-in/plug-in framework). Also, it's a very good way to componentize your application's architecture and make components/layers pluggable and replacible. Here's a very good overview of what MEF actually is with nice examples and excellent comments from readers:

Go grab it here: The download contains MEF itself (ComponentModel.dll) and several interesting samples.