IManagedAddin

This interface was introduced in Office 2007.
Any assembly that loads a managed add-in must implement this interface
This interface was designed specifically to work alongside the VSTO runtime.

In theory because this is an interface you could use itto create your own add-in loader instead of using the VSTOLoader.dll and VSTO Runtime
The CLSID for the DLL that contains this interface however is the same as the one used by VSTOLoader.dll
This basically means that deploying your own add-in loader would break any existing VSTO add-ins