By the looks of things, a "handy" homeowner glued a tub drain in place well over 20 years ago. The metal is now so corroded and brittle that it's falling apart with minimal amount of pressure. It has no crossbars for a drain key, it's too brittle for an extractor, and there's barely any metal left for pliers (just a bit where the threads were glued). I'm at a complete loss as for how to remove this thing.
Get a hacksaw blade and slowly cut a vertical slot in the metal. Check the cut often because you don't want to cut into the threads, just touch them. Then try to bend outward at the cut. If it doesn't break at that point, cut another slot the same way about an inch away from the first slot and pry that section out.
I've successfully used what I call an inside-out pipe wrench. It grabs the inside of a pipe.
The correct name is a Drain Key. It was a little awkward to use but it works. There are other models and versions.