The Open Astronomy Catalogs website (astrocats.space, including the Open Supernova, Tidal Disruption, Kilonova, Nova, Black Hole and Fast Stars catalogs and all of their subdomains) and the Open Astronomy Catalog API (OACAPI, api.astrocats.space) have been permanently retired and are no longer online.
Thank you to everyone who contributed data, code and feedback over the years.
All of the catalog data and the software used to build them remain freely available in the astrocatalogs GitHub organization. The repositories are listed below, grouped by type.
If you used the astroquery.oac module, note that it depends on the retired API and is being removed from astroquery (astropy/astroquery#3686).