It seems that CASTOR is no more.
shutdown
Epic Games Phases Out SketchFab in 2025, Launches Unified Fab Marketplace
There are big changes ahead for SketchFab.
Clara.io Shuts Down
Online 3D modeling tool Clara.io is shutting down.
MakePrintable Shuts Down!
An unexpected announcement from MakePrintable indicates the service is shutting down.
Wither Makergear? Long Time 3D Printer Manufacturer on the Ropes
Things aren’t looking good for Makergear, one of the original desktop 3D printer companies.