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?
Definitely a flaring tool for creating flared ends for copper or soft metal tubing. It was a tool they were still teaching us to use in automotive classes in the late 1980s.
We learned how to make single layer flares and double layer flares with those.
Learned all of it and then never needed to use one ever.
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.
I got really good with one because when I was young I'd always forget to put the flare nut on first lol. End up doing it twice every time. My uncle used to get pissed.