Managed Extensibility Framework (MEF)
In yesterday session "What's new in CLR 4.0" Microsoft guys presented new Managed Extensibility Framework.
Which is going to be a part of .NET 4.0.
"Application requirements change frequently and software is constantly evolving. As a result, such applications often become monolithic making it difficult to add new functionality. The Managed Extensibility Framework (MEF) is a new library in .NET Framework 4.0 that addresses this problem by simplifying the design of extensible applications and components."
Of course they introduce it as totally new apporoach to development and architecture, but in my opinion it is yet another dependency injection framework.
In any case it is nice to see it as builtin part of .NET 4.0.
Welcome to MEF!.