Anyone know if there was ever a chainsaw made, so that it could be hooked up to the 3 point hitch on a tractor, and run off the hydraulic lines ? Sure would make for easy cutting of firewood logs !

Haven't seen one, have seen a buzz saw for firewood though.

not sure about on a 3point hitch

there are a number of firewood processors that operate on the bucket attachment

Yes, an 80 year old friend of mine has a chainsaw that runs on tractor hydrological power. It was his dad's that was killed by a widow maker when Bud was about 10 logging with his dad when he was killed. I don't know any more about the saw he breafly pointed it out when he was showing of his 80or so international tractors to me.

Stihl makes an electric one with a 5 '6'" bar that you could convert to a PTO one using an angle gearbox. We used those saws to cut complete packets of lumber to length. it was on 2 wheels and worked with a hydraulic cylinder and a throttle valve to lower the bar slow enough to cut through those packets. I think the bar length was 72" and had different teeth on it than a normal chainsaw bar. Took me hours to sharpen the darn thing.

Seen one in my lifetime at an auction sale 3 point hitch pto driven six foot bar with heavy chain No one there knew anything about it

Here's one:
https://www.youtube.com/watch?v=zsJAUkJclS4
Looks good for smaller stuff.
Needs a better infeed, imo.

I have seen a firewood processor on a bigger scale for rent in Elkton,VA. The neighbors use one similar to it to make firewood.