The FEL accumulator is a combination spring and damping system for the lift arms.
Sometimes it is selectable on/off and also selectable rate
Some tractors come with an accumulator OEM installed with names like "easy ride".
We have that on our large JD.
On others you can add it as a kit. Larger Kubotas offer a kit. In fact I've got an OEM kit in the shop that may go on the
M59 someday....maybe....
In use, you can see the lift arms move up and down - sorta like floating - a few inches when it hits a bump, but the lift arm movement doesn't shake the rest of the tractor.
3pts don't have any springing or damping at all except whatever is provided by the back tires... I guess they could, but I've never seen it. I'd bet some of the fancy European tractors have it though. On compact & utility size tractors here the 3pt arms are just hydraulic lift up and gravity down. Unless you add a kit yourself. The kits aren't expensive.
rScotty