ontohub.org, spechub.org and model-hub.org

[tillmo]

Each instance should link to the other instances. Maybe provide a field in the settings where a suitable text and links can be inserted?

[tillmo]

Actuallly, there could be one instance serving all three domains. The different domains just would change between "ontology", "model" and "specification". Possibly, repositories could be classified as "ontology", "model" or "specification". But having all served by one server would have the advantage of all being searchable at once.
(Still, the links would be useful.)
Then, repositories should get a type, which can be onto, spec, or model. On domain xxxhub.org, by default only repositories of type xxx should be shown. Also ontologies should get a type (onto, spec, or model), which is by default inherited from the repository (but the user can override the default). This could be realised as single table inheritance in rails.