A central part of the CMF product, CMFCore provides much of the infrastructure on which applications such as CMFDefault, Plone, and CPS are built.
It provides some CMFTools such as the SkinsTool? and DirectoryView? (especially the latter is very usable even outside of CMF).
It does not provide any ContentTypes. These are left to the application layer, such as CMFDefault, Plone, or CPS.