>>Managed Extensibility Framework. It is not really a framework but a mechanism for extending .NET (hence the name). It falls into a category called inversion of control or dependency injection. The gist of it is compliant helpers are discovered at runtime. One of the most memorable demos I have ever seen was a couple of years ago at a .NET user group meeting. The presenter showed a simplified app which used MEF. It used a Windows timer call to discover files in a given folder. The folder consisted of pictures of animals. He added a picture of an elephant and voila, an elephant appeared on the form. No code change, no recompilation. Now that was cool.
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>Thanks, but I believe this is something we could do since about 20 years.

Possible, but not easy.

Unless I am missing something. :(

Mike's example is a simple demonstration. Imagine dropping a DLL into a folder and having it immediately incorporated into an already running application - adding it's own menu, toolbar etc on the fly. Delete it and the functionality is gone.