I'm trying to get a clear view of the roles of different components here, this is not a "which is better" comparison, these components have different roles, but their functions overlap.
(Comparing different open source GIS servers? would be an answer if it included GeoNode, CKAN and Geonetwork, it links to this excellent table: http://www.geotests.net/cours/sigma/webmapping/2013/tableau6_webmapping2013.pdf)
So, can anyone help me fill in the holes / correct this table:
Y = Yes, N = No, < = handled by included subcomponent
"Catalog data": provide searchable web / web-map front end view.
GeoNode and GeoNetwork use GeoServer for rendering and nominally WMS etc.
CKAN uses pycsw for metadata federation.