The Euro-VO Registry
The ESDC built a full harvestable VO Resource Registry, which later turned into the official Euro-VO Registry. You can access the Euro-VO Registry directly here.
A Resource Registry is defined by the IVOA as "[...]allowing an astronomer to be able to locate, get details of, and make use of, any resource located anywhere in the IVO space, ie in any Virtual Observatory. The IVOA will define the protocols and standards whereby different registry services are able to interoperate and thereby realise this goal."