I feel like I knew what this thing was right up until I had one. Two tool id site had no idea, and one said it’s a ball joint separator, but I can’t find any that look like this, and I swear I’ve seen them in stores, but can’t remember where.
Maybe a type of bearing press?
We still use them all the time in HVAC-R for refrigerant piping. Flare fittings are one of the best and easiest ways to have a reliably leak free but still easily removable connection.