The ExplorerManager class is exposed by ExplorerFrame.dll through its DllGetClassObject function. Instances are creatable, using such well-documented COM functions as CoCreateInstance, by anyone who knows the CLSID:

CLSID_ExplorerManager {1F849CCE-2546-4B9F-B03E-4004781BDC40}

The class implements only one interface. Its name as given by Microsoft is not known, though IExplorerManager seems a good guess.