Sign-up for an account at this URL:

http://www.aiai.ed.ac.uk/project/cobra-ct/COBrA_downloads.htm

Use this form to apply for a user account on the COBrA-CT ontology server. With an account name and password you can upload ontologies, and share them with other registered users.

If you prefer not to register, you can still use the system as a guest. This enables you to download all ontologies that have been declared public.