Exensible application shell for Windows Forms

We're about to start development of an in-house WinForms app (no WPF here), and I'm looking for a kind of an extensible "shell" application, which would take care of all the low-level stuff like menu & toolba开发者_运维问答r management, dialogs, etc. Pretty much like Visual Studio Shell:

What it should do is to allow us to write some kind of "add-ins" which would use services provided by this "shell" and do all the business stuff.

---

How about Composite Application Block?. Check the examples on the Internet, and see if that is what you want. It is not really a app. shell but more of a architecture to build complex app around; but the notion of application shell and loosely coupled parts are main theme in CAB (check Event Dispatcher among other things)